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/user_handler.go

@@ -486,7 +486,7 @@ func (h *UserHandler) ListUsers(c *fiber.Ctx) error {
 
 			// Expand manageableSlugs to the entire tenant tree (root + all descendants)
 			if h.TenantService != nil && len(baseTenantIDs) > 0 {
-				allTenants, _, err := h.TenantService.ListTenants(c.Context(), 10000, 0, "")
+				allTenants, _, err := h.TenantService.ListTenants(c.Context(), 10000, 0, "", "")
 				if err == nil {
 					parentMap := make(map[string]string)
 					for _, t := range allTenants {
@@ -1614,7 +1614,7 @@ func (h *UserHandler) ExportUsersCSV(c *fiber.Ctx) error {
 	}
 
 	// 1. Fetch Users using Repo for efficiency
-	users, _, err := h.UserRepo.List(c.Context(), 0, 10000, search, tenantSlug)
+	users, _, _, err := h.UserRepo.List(c.Context(), 0, 10000, search, tenantSlug, "")
 	if err != nil {
 		return errorJSON(c, fiber.StatusInternalServerError, "failed to fetch users for export")
 	}