feat(admin): Add group filtering for account listings

- Add groupID parameter to ListAccounts and ListWithFilters methods
- Implement account filtering by group ID in repository query
- Add group query parameter parsing in account handler
- Update all ListAccounts/ListWithFilters call sites with groupID parameter
- Add group filter UI component to AccountTableFilters
- Add i18n translations for group filter label in English and Chinese
- Update API contract and test stubs to reflect new signature
- Enable filtering accounts by their assigned groups in admin panel

frontend/src/api/admin/accounts.ts

@@ -32,6 +32,7 @@ export async function list(
     platform?: string
     type?: string
     status?: string
+    group?: string
     search?: string
   },
   options?: {