perf(admin): implement server-side search and virtualization for tenant list

- Backend: Added 'search' parameter to TenantRepository and TenantService.
- Backend: Updated all Tenant list calls to support searching.
- Backend: Enhanced UserRepository.List to support cursor-based pagination and search.
- Frontend: Switched TenantListPage to use useInfiniteQuery for lazy loading.
- Frontend: Implemented list virtualization in TenantHierarchyView using @tanstack/react-virtual.
- Frontend: Added server-side search with debouncing (useDeferredValue).
- Fixed various Go compilation errors caused by method signature changes.

backend/internal/handler/admin_handler.go

@@ -235,7 +235,7 @@ func (h *AdminHandler) countTenants(ctx context.Context) int64 {
 	if h == nil || h.TenantRepo == nil {
 		return 0
 	}
-	_, total, err := h.TenantRepo.List(ctx, 1, 0, "")
+	_, total, err := h.TenantRepo.List(ctx, 1, 0, "", "")
 	if err != nil {
 		return 0
 	}