feat(T01): auth + user management + RBAC + base frontend + i18n

- Backend: FastAPI, JWT auth (HS256), bcrypt, RBAC middleware
- User CRUD (admin-only), soft-delete, pagination
- Pydantic BaseSettings config, async SQLAlchemy 2.0
- 50 backend tests, 88% coverage
- Frontend: Next.js 14 App Router, Tailwind, design tokens
- Login page, auth context, API client with auto-refresh
- i18n: next-intl, DE/EN (31 keys each)
- 6 base UI components (Button, Input, Card, Table, Modal, Toast)
- 12 frontend tests, npm build success

frontend/tests/setup.ts

@@ -0,0 +1,15 @@
+import '@testing-library/jest-dom';
+import { vi } from 'vitest';
+
+// Mock next/navigation globally
+vi.mock('next/navigation', () => ({
+  useRouter: () => ({
+    push: vi.fn(),
+    replace: vi.fn(),
+    back: vi.fn(),
+    refresh: vi.fn(),
+  }),
+  redirect: vi.fn(),
+  usePathname: () => '/login',
+  useSearchParams: () => new URLSearchParams(),
+}));