feat(usage): add account cost display to admin dashboard and usage pages

- Add account_cost column to dashboard aggregation tables (migration 107)
- DashboardStats: add TotalAccountCost/TodayAccountCost fields
- ModelStat/GroupStat: add AccountCost field with SQL aggregation
- GetStatsWithFilters: always return TotalAccountCost (remove accountID filter)
- Dashboard Token cards: show user(green)/cost(orange)/standard(gray)
- Usage stats card: show account cost and standard below main value
- Model/Group distribution tables: add orange cost column

frontend/src/components/charts/ModelDistributionChart.vue

@@ -114,6 +114,7 @@
               <th class="pb-2 text-right">{{ t('admin.dashboard.requests') }}</th>
               <th class="pb-2 text-right">{{ t('admin.dashboard.tokens') }}</th>
               <th class="pb-2 text-right">{{ t('admin.dashboard.actual') }}</th>
+              <th class="pb-2 text-right">{{ t('admin.dashboard.accountCost') }}</th>
               <th class="pb-2 text-right">{{ t('admin.dashboard.standard') }}</th>
             </tr>
           </thead>
@@ -142,12 +143,15 @@
                 <td class="py-1.5 text-right text-green-600 dark:text-green-400">
                   ${{ formatCost(model.actual_cost) }}
                 </td>
+                <td class="py-1.5 text-right text-orange-500 dark:text-orange-400">
+                  ${{ formatCost(model.account_cost) }}
+                </td>
                 <td class="py-1.5 text-right text-gray-400 dark:text-gray-500">
                   ${{ formatCost(model.cost) }}
                 </td>
               </tr>
               <tr v-if="expandedKey === `model-${model.model}`">
-                <td colspan="5" class="p-0">
+                <td colspan="6" class="p-0">
                   <UserBreakdownSubTable
                     :items="breakdownItems"
                     :loading="breakdownLoading"