feat(layout): finalize p01 and p02 changes

Complete UI foundation and app layout implementation, stabilize container health checks, and archive both OpenSpec changes after verification.

frontend/tests/setup.ts

@@ -1,13 +1,19 @@
 import { vi } from 'vitest';
 
 // Mock localStorage
-global.localStorage = {
+const localStorageMock: Storage = {
+  get length() {
+    return 0;
+  },
+  key: vi.fn(() => null),
   getItem: vi.fn(),
   setItem: vi.fn(),
   removeItem: vi.fn(),
   clear: vi.fn(),
 };
 
+global.localStorage = localStorageMock;
+
 // Mock fetch
 global.fetch = vi.fn();