refactor(frontend): comprehensive split of large view files into modular components

- Split UsersView.vue into UserCreateModal, UserEditModal, UserApiKeysModal, etc.
- Split UsageView.vue into UsageStatsCards, UsageFilters, UsageTable, etc.
- Split DashboardView.vue into UserDashboardStats, UserDashboardCharts, etc.
- Split AccountsView.vue into AccountTableActions, AccountTableFilters, etc.
- Standardized TypeScript types across new components to resolve implicit 'any' and 'never[]' errors.
- Improved overall frontend maintainability and code clarity.

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

@@ -0,0 +1,46 @@
+<template>
+  <BaseDialog :show="show" :title="operation === 'add' ? t('admin.users.deposit') : t('admin.users.withdraw')" width="narrow" @close="$emit('close')">
+    <form v-if="user" id="balance-form" @submit.prevent="handleBalanceSubmit" class="space-y-5">
+      <div class="flex items-center gap-3 rounded-xl bg-gray-50 p-4 dark:bg-dark-700">
+        <div class="flex h-10 w-10 items-center justify-center rounded-full bg-primary-100"><span class="text-lg font-medium text-primary-700">{{ user.email.charAt(0).toUpperCase() }}</span></div>
+        <div class="flex-1"><p class="font-medium text-gray-900">{{ user.email }}</p><p class="text-sm text-gray-500">{{ t('admin.users.currentBalance') }}: ${{ user.balance.toFixed(2) }}</p></div>
+      </div>
+      <div>
+        <label class="input-label">{{ operation === 'add' ? t('admin.users.depositAmount') : t('admin.users.withdrawAmount') }}</label>
+        <div class="relative"><div class="absolute left-3 top-1/2 -translate-y-1/2 font-medium text-gray-500">$</div><input v-model.number="form.amount" type="number" step="0.01" min="0.01" required class="input pl-8" /></div>
+      </div>
+      <div><label class="input-label">{{ t('admin.users.notes') }}</label><textarea v-model="form.notes" rows="3" class="input"></textarea></div>
+      <div v-if="form.amount > 0" class="rounded-xl border border-blue-200 bg-blue-50 p-4"><div class="flex items-center justify-between text-sm"><span>{{ t('admin.users.newBalance') }}:</span><span class="font-bold">${{ calculateNewBalance().toFixed(2) }}</span></div></div>
+    </form>
+    <template #footer>
+      <div class="flex justify-end gap-3">
+        <button @click="$emit('close')" class="btn btn-secondary">{{ t('common.cancel') }}</button>
+        <button type="submit" form="balance-form" :disabled="submitting || !form.amount" class="btn" :class="operation === 'add' ? 'bg-emerald-600 text-white' : 'btn-danger'">{{ submitting ? t('common.saving') : t('common.confirm') }}</button>
+      </div>
+    </template>
+  </BaseDialog>
+</template>
+
+<script setup lang="ts">
+import { reactive, ref, watch } from 'vue'
+import { useI18n } from 'vue-i18n'
+import { useAppStore } from '@/stores/app'
+import { adminAPI } from '@/api/admin'
+import type { User } from '@/types'
+import BaseDialog from '@/components/common/BaseDialog.vue'
+
+const props = defineProps<{ show: boolean, user: User | null, operation: 'add' | 'subtract' }>()
+const emit = defineEmits(['close', 'success']); const { t } = useI18n(); const appStore = useAppStore()
+
+const submitting = ref(false); const form = reactive({ amount: 0, notes: '' })
+watch(() => props.show, (v) => { if(v) { form.amount = 0; form.notes = '' } })
+
+const calculateNewBalance = () => (props.user ? (props.operation === 'add' ? props.user.balance + form.amount : props.user.balance - form.amount) : 0)
+const handleBalanceSubmit = async () => {
+  if (!props.user) return; submitting.value = true
+  try {
+    await adminAPI.users.updateBalance(props.user.id, form.amount, props.operation, form.notes)
+    appStore.showSuccess(t('common.success')); emit('success'); emit('close')
+  } catch {} finally { submitting.value = false }
+}
+</script>