feat(usage): add account cost to breakdown sub-table and admin usage log

- UserBreakdownItem: add AccountCost field + SQL aggregation
- UserBreakdownSubTable: add orange account cost column
- Admin usage table: add account_cost column (after cost, default visible)
- Column settings: add account_cost toggle option

frontend/src/components/admin/usage/UsageTable.vue

@@ -160,6 +160,12 @@
           </div>
         </template>
 
+        <template #cell-account_cost="{ row }">
+          <span class="text-sm font-medium text-orange-500 dark:text-orange-400">
+            ${{ accountBilled(row).toFixed(6) }}
+          </span>
+        </template>
+
         <template #cell-first_token="{ row }">
           <span v-if="row.first_token_ms != null" class="text-sm text-gray-600 dark:text-gray-400">{{ formatDuration(row.first_token_ms) }}</span>
           <span v-else class="text-sm text-gray-400 dark:text-gray-500">-</span>

frontend/src/components/charts/UserBreakdownSubTable.vue

@@ -25,6 +25,9 @@
           <td class="py-1 text-right text-green-600 dark:text-green-400">
             ${{ formatCost(user.actual_cost) }}
           </td>
+          <td class="py-1 text-right text-orange-500 dark:text-orange-400">
+            ${{ formatCost(user.account_cost) }}
+          </td>
           <td class="py-1 pr-1 text-right text-gray-400 dark:text-gray-500">
             ${{ formatCost(user.cost) }}
           </td>

frontend/src/types/index.ts

@@ -1245,6 +1245,7 @@ export interface UserBreakdownItem {
   total_tokens: number
   cost: number
   actual_cost: number
+  account_cost: number
 }
 
 export interface UserUsageTrendPoint {

frontend/src/views/admin/UsageView.vue

@@ -533,6 +533,7 @@ const allColumns = computed(() => [
   { key: 'billing_mode', label: t('admin.usage.billingMode'), sortable: false },
   { key: 'tokens', label: t('usage.tokens'), sortable: false },
   { key: 'cost', label: t('usage.cost'), sortable: false },
+  { key: 'account_cost', label: t('usage.accountCost'), sortable: false },
   { key: 'first_token', label: t('usage.firstToken'), sortable: false },
   { key: 'duration', label: t('usage.duration'), sortable: false },
   { key: 'created_at', label: t('usage.time'), sortable: true },