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

backend/internal/repository/account_repo.go

@@ -435,10 +435,10 @@ func (r *accountRepository) Delete(ctx context.Context, id int64) error {
 }
 
 func (r *accountRepository) List(ctx context.Context, params pagination.PaginationParams) ([]service.Account, *pagination.PaginationResult, error) {
-	return r.ListWithFilters(ctx, params, "", "", "", "")
+	return r.ListWithFilters(ctx, params, "", "", "", "", 0)
 }
 
-func (r *accountRepository) ListWithFilters(ctx context.Context, params pagination.PaginationParams, platform, accountType, status, search string) ([]service.Account, *pagination.PaginationResult, error) {
+func (r *accountRepository) ListWithFilters(ctx context.Context, params pagination.PaginationParams, platform, accountType, status, search string, groupID int64) ([]service.Account, *pagination.PaginationResult, error) {
 	q := r.client.Account.Query()
 
 	if platform != "" {
@@ -458,6 +458,9 @@ func (r *accountRepository) ListWithFilters(ctx context.Context, params paginati
 	if search != "" {
 		q = q.Where(dbaccount.NameContainsFold(search))
 	}
+	if groupID > 0 {
+		q = q.Where(dbaccount.HasAccountGroupsWith(dbaccountgroup.GroupIDEQ(groupID)))
+	}
 
 	total, err := q.Count(ctx)
 	if err != nil {