docs: update pipeline rules for user menu implementation

- Added critical guidelines prohibiting the direct creation of user menu screens in React (.tsx) files, emphasizing that user menus must be implemented through database registration methods (screen_definitions, screen_layouts_v2, menu_info).
- Clarified that backend agents should not request or suggest the creation of frontend pages for user menus.
- Reinforced the importance of adhering to the established rendering system to prevent hardcoding UI components.

Made-with: Cursor

frontend/components/layout/AppLayout.tsx

@@ -362,8 +362,10 @@ function AppLayoutInner({ children }: AppLayoutProps) {
           if (isMobile) setSidebarOpen(false);
           return;
         }
-      } catch {
-        console.warn("할당된 화면 조회 실패");
+      } catch (err) {
+        console.error("할당된 화면 조회 실패:", err);
+        toast.error("화면 정보를 불러오지 못했습니다. 다시 시도해주세요.");
+        return;
       }
 
       if (menu.url && menu.url !== "#") {