feat: admin bulk actions page with TanStack Table

Full-featured admin page for mass operations on users:

- TanStack Table with checkbox selection (select all / individual)
- Server-side pagination, search, and filters (status, tariff, promo group)
- Columns: user, subscription status, tariff, balance, days left, promo group
- Floating glass-effect action bar with 7 bulk operations:
  extend subscription, deactivate, activate, change tariff,
  add traffic, add balance, assign promo group
- Action modal dialogs with input fields, loading state, result summary
- Responsive design for desktop, mobile, and Telegram Mini App
- Full i18n support (ru, en)
- Dark theme with accent highlights and status color badges

src/App.tsx

@@ -123,6 +123,7 @@ const AdminRemnawave = lazyWithRetry(() => import('./pages/AdminRemnawave'));
 const AdminRemnawaveSquadDetail = lazyWithRetry(() => import('./pages/AdminRemnawaveSquadDetail'));
 const AdminEmailTemplates = lazyWithRetry(() => import('./pages/AdminEmailTemplates'));
 const AdminTrafficUsage = lazyWithRetry(() => import('./pages/AdminTrafficUsage'));
+const AdminBulkActions = lazyWithRetry(() => import('./pages/AdminBulkActions'));
 const AdminSalesStats = lazyWithRetry(() => import('./pages/AdminSalesStats'));
 const AdminUpdates = lazyWithRetry(() => import('./pages/AdminUpdates'));
 const AdminUserDetail = lazyWithRetry(() => import('./pages/AdminUserDetail'));
@@ -966,6 +967,16 @@ function App() {
             </PermissionRoute>
           }
         />
+        <Route
+          path="/admin/bulk-actions"
+          element={
+            <PermissionRoute permission="users:read">
+              <LazyPage>
+                <AdminBulkActions />
+              </LazyPage>
+            </PermissionRoute>
+          }
+        />
         <Route
           path="/admin/payments"
           element={