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/api/adminBulkActions.ts

@@ -0,0 +1,42 @@
+import apiClient from './client';
+
+export type BulkActionType =
+  | 'extend'
+  | 'cancel'
+  | 'activate'
+  | 'change_tariff'
+  | 'add_traffic'
+  | 'add_balance'
+  | 'assign_promo_group';
+
+export interface BulkActionRequest {
+  action: BulkActionType;
+  user_ids: number[];
+  params: BulkActionParams;
+}
+
+export interface BulkActionParams {
+  days?: number;
+  tariff_id?: number;
+  traffic_gb?: number;
+  balance_kopeks?: number;
+  promo_group_id?: number | null;
+}
+
+export interface BulkActionResult {
+  success: boolean;
+  total: number;
+  success_count: number;
+  error_count: number;
+  errors: Array<{
+    user_id: number;
+    error: string;
+  }>;
+}
+
+export const adminBulkActionsApi = {
+  execute: async (data: BulkActionRequest): Promise<BulkActionResult> => {
+    const response = await apiClient.post('/cabinet/admin/bulk/execute', data);
+    return response.data;
+  },
+};