feat(admin): add user balance/concurrency history modal

- Add new API endpoint GET /admin/users/:id/balance-history with pagination and type filter
- Add SumPositiveBalanceByUser for calculating total recharged amount
- Create UserBalanceHistoryModal component with:
  - User info header (email, username, created_at, current balance, notes, total recharged)
  - Type filter dropdown (all/balance/admin_balance/concurrency/admin_concurrency/subscription)
  - Quick deposit/withdraw buttons
  - Paginated history list with icons and colored values
- Add instant tooltip on balance column for better UX
- Add z-index prop to BaseDialog for modal stacking control
- Update i18n translations (zh/en)

frontend/src/components/admin/user/UserBalanceHistoryModal.vue

@@ -0,0 +1,320 @@
+<template>
+  <BaseDialog :show="show" :title="t('admin.users.balanceHistoryTitle')" width="wide" :close-on-click-outside="true" :z-index="40" @close="$emit('close')">
+    <div v-if="user" class="space-y-4">
+      <!-- User header: two-row layout with full user info -->
+      <div class="rounded-xl bg-gray-50 p-4 dark:bg-dark-700">
+        <!-- Row 1: avatar + email/username/created_at (left) + current balance (right) -->
+        <div class="flex items-center gap-3">
+          <div class="flex h-10 w-10 flex-shrink-0 items-center justify-center rounded-full bg-primary-100 dark:bg-primary-900/30">
+            <span class="text-lg font-medium text-primary-700 dark:text-primary-300">
+              {{ user.email.charAt(0).toUpperCase() }}
+            </span>
+          </div>
+          <div class="min-w-0 flex-1">
+            <div class="flex items-center gap-2">
+              <p class="truncate font-medium text-gray-900 dark:text-white">{{ user.email }}</p>
+              <span
+                v-if="user.username"
+                class="flex-shrink-0 rounded bg-primary-50 px-1.5 py-0.5 text-xs text-primary-600 dark:bg-primary-900/20 dark:text-primary-400"
+              >
+                {{ user.username }}
+              </span>
+            </div>
+            <p class="text-xs text-gray-400 dark:text-dark-500">
+              {{ t('admin.users.createdAt') }}: {{ formatDateTime(user.created_at) }}
+            </p>
+          </div>
+          <!-- Current balance: prominent display on the right -->
+          <div class="flex-shrink-0 text-right">
+            <p class="text-xs text-gray-500 dark:text-dark-400">{{ t('admin.users.currentBalance') }}</p>
+            <p class="text-xl font-bold text-gray-900 dark:text-white">
+              ${{ user.balance?.toFixed(2) || '0.00' }}
+            </p>
+          </div>
+        </div>
+        <!-- Row 2: notes + total recharged -->
+        <div class="mt-2.5 flex items-center justify-between border-t border-gray-200/60 pt-2.5 dark:border-dark-600/60">
+          <p class="min-w-0 flex-1 truncate text-xs text-gray-500 dark:text-dark-400" :title="user.notes || ''">
+            <template v-if="user.notes">{{ t('admin.users.notes') }}: {{ user.notes }}</template>
+            <template v-else>&nbsp;</template>
+          </p>
+          <p class="ml-4 flex-shrink-0 text-xs text-gray-500 dark:text-dark-400">
+            {{ t('admin.users.totalRecharged') }}: <span class="font-semibold text-emerald-600 dark:text-emerald-400">${{ totalRecharged.toFixed(2) }}</span>
+          </p>
+        </div>
+      </div>
+
+      <!-- Type filter + Action buttons -->
+      <div class="flex items-center gap-3">
+        <Select
+          v-model="typeFilter"
+          :options="typeOptions"
+          class="w-56"
+          @change="loadHistory(1)"
+        />
+        <!-- Deposit button - matches menu style -->
+        <button
+          @click="emit('deposit')"
+          class="flex items-center gap-2 rounded-lg border border-gray-200 bg-white px-3 py-2 text-sm text-gray-700 transition-colors hover:bg-gray-50 dark:border-dark-600 dark:bg-dark-800 dark:text-gray-300 dark:hover:bg-dark-700"
+        >
+          <Icon name="plus" size="sm" class="text-emerald-500" :stroke-width="2" />
+          {{ t('admin.users.deposit') }}
+        </button>
+        <!-- Withdraw button - matches menu style -->
+        <button
+          @click="emit('withdraw')"
+          class="flex items-center gap-2 rounded-lg border border-gray-200 bg-white px-3 py-2 text-sm text-gray-700 transition-colors hover:bg-gray-50 dark:border-dark-600 dark:bg-dark-800 dark:text-gray-300 dark:hover:bg-dark-700"
+        >
+          <svg class="h-4 w-4 text-amber-500" fill="none" viewBox="0 0 24 24" stroke="currentColor">
+            <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M20 12H4" />
+          </svg>
+          {{ t('admin.users.withdraw') }}
+        </button>
+      </div>
+
+      <!-- Loading -->
+      <div v-if="loading" class="flex justify-center py-8">
+        <svg class="h-8 w-8 animate-spin text-primary-500" fill="none" viewBox="0 0 24 24">
+          <circle class="opacity-25" cx="12" cy="12" r="10" stroke="currentColor" stroke-width="4" />
+          <path class="opacity-75" fill="currentColor" d="M4 12a8 8 0 018-8V0C5.373 0 0 5.373 0 12h4zm2 5.291A7.962 7.962 0 014 12H0c0 3.042 1.135 5.824 3 7.938l3-2.647z" />
+        </svg>
+      </div>
+
+      <!-- Empty state -->
+      <div v-else-if="history.length === 0" class="py-8 text-center">
+        <p class="text-sm text-gray-500">{{ t('admin.users.noBalanceHistory') }}</p>
+      </div>
+
+      <!-- History list -->
+      <div v-else class="max-h-[28rem] space-y-3 overflow-y-auto">
+        <div
+          v-for="item in history"
+          :key="item.id"
+          class="rounded-xl border border-gray-200 bg-white p-4 dark:border-dark-600 dark:bg-dark-800"
+        >
+          <div class="flex items-start justify-between">
+            <!-- Left: type icon + description -->
+            <div class="flex items-start gap-3">
+              <div
+                :class="[
+                  'flex h-9 w-9 flex-shrink-0 items-center justify-center rounded-lg',
+                  getIconBg(item)
+                ]"
+              >
+                <Icon :name="getIconName(item)" size="sm" :class="getIconColor(item)" />
+              </div>
+              <div>
+                <p class="text-sm font-medium text-gray-900 dark:text-white">
+                  {{ getItemTitle(item) }}
+                </p>
+                <!-- Notes (admin adjustment reason) -->
+                <p
+                  v-if="item.notes"
+                  class="mt-0.5 text-xs text-gray-500 dark:text-dark-400"
+                  :title="item.notes"
+                >
+                  {{ item.notes.length > 60 ? item.notes.substring(0, 55) + '...' : item.notes }}
+                </p>
+                <p class="mt-0.5 text-xs text-gray-400 dark:text-dark-500">
+                  {{ formatDateTime(item.used_at || item.created_at) }}
+                </p>
+              </div>
+            </div>
+            <!-- Right: value -->
+            <div class="text-right">
+              <p :class="['text-sm font-semibold', getValueColor(item)]">
+                {{ formatValue(item) }}
+              </p>
+              <p
+                v-if="isAdminType(item.type)"
+                class="text-xs text-gray-400 dark:text-dark-500"
+              >
+                {{ t('redeem.adminAdjustment') }}
+              </p>
+              <p
+                v-else
+                class="font-mono text-xs text-gray-400 dark:text-dark-500"
+              >
+                {{ item.code.slice(0, 8) }}...
+              </p>
+            </div>
+          </div>
+        </div>
+      </div>
+
+      <!-- Pagination -->
+      <div v-if="totalPages > 1" class="flex items-center justify-center gap-2 pt-2">
+        <button
+          :disabled="currentPage <= 1"
+          class="btn btn-secondary px-3 py-1 text-sm"
+          @click="loadHistory(currentPage - 1)"
+        >
+          {{ t('pagination.previous') }}
+        </button>
+        <span class="text-sm text-gray-500 dark:text-dark-400">
+          {{ currentPage }} / {{ totalPages }}
+        </span>
+        <button
+          :disabled="currentPage >= totalPages"
+          class="btn btn-secondary px-3 py-1 text-sm"
+          @click="loadHistory(currentPage + 1)"
+        >
+          {{ t('pagination.next') }}
+        </button>
+      </div>
+    </div>
+  </BaseDialog>
+</template>
+
+<script setup lang="ts">
+import { ref, computed, watch } from 'vue'
+import { useI18n } from 'vue-i18n'
+import { adminAPI, type BalanceHistoryItem } from '@/api/admin'
+import { formatDateTime } from '@/utils/format'
+import type { AdminUser } from '@/types'
+import BaseDialog from '@/components/common/BaseDialog.vue'
+import Select from '@/components/common/Select.vue'
+import Icon from '@/components/icons/Icon.vue'
+
+const props = defineProps<{ show: boolean; user: AdminUser | null }>()
+const emit = defineEmits(['close', 'deposit', 'withdraw'])
+const { t } = useI18n()
+
+const history = ref<BalanceHistoryItem[]>([])
+const loading = ref(false)
+const currentPage = ref(1)
+const total = ref(0)
+const totalRecharged = ref(0)
+const pageSize = 15
+const typeFilter = ref('')
+
+const totalPages = computed(() => Math.ceil(total.value / pageSize) || 1)
+
+// Type filter options
+const typeOptions = computed(() => [
+  { value: '', label: t('admin.users.allTypes') },
+  { value: 'balance', label: t('admin.users.typeBalance') },
+  { value: 'admin_balance', label: t('admin.users.typeAdminBalance') },
+  { value: 'concurrency', label: t('admin.users.typeConcurrency') },
+  { value: 'admin_concurrency', label: t('admin.users.typeAdminConcurrency') },
+  { value: 'subscription', label: t('admin.users.typeSubscription') }
+])
+
+// Watch modal open
+watch(() => props.show, (v) => {
+  if (v && props.user) {
+    typeFilter.value = ''
+    loadHistory(1)
+  }
+})
+
+const loadHistory = async (page: number) => {
+  if (!props.user) return
+  loading.value = true
+  currentPage.value = page
+  try {
+    const res = await adminAPI.users.getUserBalanceHistory(
+      props.user.id,
+      page,
+      pageSize,
+      typeFilter.value || undefined
+    )
+    history.value = res.items || []
+    total.value = res.total || 0
+    totalRecharged.value = res.total_recharged || 0
+  } catch (error) {
+    console.error('Failed to load balance history:', error)
+  } finally {
+    loading.value = false
+  }
+}
+
+// Helper: check if admin type
+const isAdminType = (type: string) => type === 'admin_balance' || type === 'admin_concurrency'
+
+// Helper: check if balance type (includes admin_balance)
+const isBalanceType = (type: string) => type === 'balance' || type === 'admin_balance'
+
+// Helper: check if subscription type
+const isSubscriptionType = (type: string) => type === 'subscription'
+
+// Icon name based on type
+const getIconName = (item: BalanceHistoryItem) => {
+  if (isBalanceType(item.type)) return 'dollar'
+  if (isSubscriptionType(item.type)) return 'badge'
+  return 'bolt' // concurrency
+}
+
+// Icon background color
+const getIconBg = (item: BalanceHistoryItem) => {
+  if (isBalanceType(item.type)) {
+    return item.value >= 0
+      ? 'bg-emerald-100 dark:bg-emerald-900/30'
+      : 'bg-red-100 dark:bg-red-900/30'
+  }
+  if (isSubscriptionType(item.type)) return 'bg-purple-100 dark:bg-purple-900/30'
+  return item.value >= 0
+    ? 'bg-blue-100 dark:bg-blue-900/30'
+    : 'bg-orange-100 dark:bg-orange-900/30'
+}
+
+// Icon text color
+const getIconColor = (item: BalanceHistoryItem) => {
+  if (isBalanceType(item.type)) {
+    return item.value >= 0
+      ? 'text-emerald-600 dark:text-emerald-400'
+      : 'text-red-600 dark:text-red-400'
+  }
+  if (isSubscriptionType(item.type)) return 'text-purple-600 dark:text-purple-400'
+  return item.value >= 0
+    ? 'text-blue-600 dark:text-blue-400'
+    : 'text-orange-600 dark:text-orange-400'
+}
+
+// Value text color
+const getValueColor = (item: BalanceHistoryItem) => {
+  if (isBalanceType(item.type)) {
+    return item.value >= 0
+      ? 'text-emerald-600 dark:text-emerald-400'
+      : 'text-red-600 dark:text-red-400'
+  }
+  if (isSubscriptionType(item.type)) return 'text-purple-600 dark:text-purple-400'
+  return item.value >= 0
+    ? 'text-blue-600 dark:text-blue-400'
+    : 'text-orange-600 dark:text-orange-400'
+}
+
+// Item title
+const getItemTitle = (item: BalanceHistoryItem) => {
+  switch (item.type) {
+    case 'balance':
+      return t('redeem.balanceAddedRedeem')
+    case 'admin_balance':
+      return item.value >= 0 ? t('redeem.balanceAddedAdmin') : t('redeem.balanceDeductedAdmin')
+    case 'concurrency':
+      return t('redeem.concurrencyAddedRedeem')
+    case 'admin_concurrency':
+      return item.value >= 0 ? t('redeem.concurrencyAddedAdmin') : t('redeem.concurrencyReducedAdmin')
+    case 'subscription':
+      return t('redeem.subscriptionAssigned')
+    default:
+      return t('common.unknown')
+  }
+}
+
+// Format display value
+const formatValue = (item: BalanceHistoryItem) => {
+  if (isBalanceType(item.type)) {
+    const sign = item.value >= 0 ? '+' : ''
+    return `${sign}$${item.value.toFixed(2)}`
+  }
+  if (isSubscriptionType(item.type)) {
+    const days = item.validity_days || Math.round(item.value)
+    const groupName = item.group?.name || ''
+    return groupName ? `${days}d - ${groupName}` : `${days}d`
+  }
+  // concurrency types
+  const sign = item.value >= 0 ? '+' : ''
+  return `${sign}${item.value}`
+}
+</script>

frontend/src/components/common/BaseDialog.vue

@@ -4,6 +4,7 @@
       <div
         v-if="show"
         class="modal-overlay"
+        :style="zIndexStyle"
         :aria-labelledby="dialogId"
         role="dialog"
         aria-modal="true"
@@ -60,6 +61,7 @@ interface Props {
   width?: DialogWidth
   closeOnEscape?: boolean
   closeOnClickOutside?: boolean
+  zIndex?: number
 }
 
 interface Emits {
@@ -69,11 +71,17 @@ interface Emits {
 const props = withDefaults(defineProps<Props>(), {
   width: 'normal',
   closeOnEscape: true,
-  closeOnClickOutside: false
+  closeOnClickOutside: false,
+  zIndex: 50
 })
 
 const emit = defineEmits<Emits>()
 
+// Custom z-index style (overrides the default z-50 from CSS)
+const zIndexStyle = computed(() => {
+  return props.zIndex !== 50 ? { zIndex: props.zIndex } : undefined
+})
+
 const widthClasses = computed(() => {
   // Width guidance: narrow=confirm/short prompts, normal=standard forms,
   // wide=multi-section forms or rich content, extra-wide=analytics/tables,