feat: 账号管理新增使用统计功能

- 新增账号统计弹窗，展示30天使用数据
- 显示总费用、请求数、日均费用、日均请求等汇总指标
- 显示今日概览、最高费用日、最高请求日
- 包含费用与请求趋势图（双Y轴）
- 复用模型分布图组件展示模型使用分布
- 显示实际扣费和标准计费（标准计费以较淡颜色显示）

frontend/src/views/admin/AccountsView.vue

@@ -186,6 +186,16 @@
                   <path stroke-linecap="round" stroke-linejoin="round" d="M5.25 5.653c0-.856.917-1.398 1.667-.986l11.54 6.347a1.125 1.125 0 010 1.972l-11.54 6.347a1.125 1.125 0 01-1.667-.986V5.653z" />
                 </svg>
               </button>
+              <!-- View Stats button -->
+              <button
+                @click="handleViewStats(row)"
+                class="p-2 rounded-lg hover:bg-indigo-50 dark:hover:bg-indigo-900/20 text-gray-500 hover:text-indigo-600 dark:hover:text-indigo-400 transition-colors"
+                :title="t('admin.accounts.viewStats')"
+              >
+                <svg class="w-4 h-4" fill="none" stroke="currentColor" viewBox="0 0 24 24" stroke-width="1.5">
+                  <path stroke-linecap="round" stroke-linejoin="round" d="M3 13.125C3 12.504 3.504 12 4.125 12h2.25c.621 0 1.125.504 1.125 1.125v6.75C7.5 20.496 6.996 21 6.375 21h-2.25A1.125 1.125 0 013 19.875v-6.75zM9.75 8.625c0-.621.504-1.125 1.125-1.125h2.25c.621 0 1.125.504 1.125 1.125v11.25c0 .621-.504 1.125-1.125 1.125h-2.25a1.125 1.125 0 01-1.125-1.125V8.625zM16.5 4.125c0-.621.504-1.125 1.125-1.125h2.25C20.496 3 21 3.504 21 4.125v15.75c0 .621-.504 1.125-1.125 1.125h-2.25a1.125 1.125 0 01-1.125-1.125V4.125z" />
+                </svg>
+              </button>
               <button
                 v-if="row.type === 'oauth' || row.type === 'setup-token'"
                 @click="handleReAuth(row)"
@@ -284,6 +294,13 @@
       @close="closeTestModal"
     />
 
+    <!-- Account Stats Modal -->
+    <AccountStatsModal
+      :show="showStatsModal"
+      :account="statsAccount"
+      @close="closeStatsModal"
+    />
+
     <!-- Delete Confirmation Dialog -->
     <ConfirmDialog
       :show="showDeleteDialog"
@@ -311,7 +328,7 @@ import Pagination from '@/components/common/Pagination.vue'
 import ConfirmDialog from '@/components/common/ConfirmDialog.vue'
 import EmptyState from '@/components/common/EmptyState.vue'
 import Select from '@/components/common/Select.vue'
-import { CreateAccountModal, EditAccountModal, ReAuthAccountModal } from '@/components/account'
+import { CreateAccountModal, EditAccountModal, ReAuthAccountModal, AccountStatsModal } from '@/components/account'
 import AccountStatusIndicator from '@/components/account/AccountStatusIndicator.vue'
 import AccountUsageCell from '@/components/account/AccountUsageCell.vue'
 import AccountTodayStatsCell from '@/components/account/AccountTodayStatsCell.vue'
@@ -382,10 +399,12 @@ const showEditModal = ref(false)
 const showReAuthModal = ref(false)
 const showDeleteDialog = ref(false)
 const showTestModal = ref(false)
+const showStatsModal = ref(false)
 const editingAccount = ref<Account | null>(null)
 const reAuthAccount = ref<Account | null>(null)
 const deletingAccount = ref<Account | null>(null)
 const testingAccount = ref<Account | null>(null)
+const statsAccount = ref<Account | null>(null)
 const togglingSchedulable = ref<number | null>(null)
 
 // Rate limit / Overload helpers
@@ -574,6 +593,17 @@ const closeTestModal = () => {
   testingAccount.value = null
 }
 
+// Stats modal
+const handleViewStats = (account: Account) => {
+  statsAccount.value = account
+  showStatsModal.value = true
+}
+
+const closeStatsModal = () => {
+  showStatsModal.value = false
+  statsAccount.value = null
+}
+
 // Initialize
 onMounted(() => {
   loadAccounts()