test(frontend): add Playwright E2E test setup

Implement Task 17: Frontend Test Infrastructure - Playwright

Configuration:
- playwright.config.ts: baseURL localhost:3000, Chromium only
- Screenshot on failure, trace on first retry
- Auto-start webServer (bun dev) if not running
- Test directory: ./e2e/

Smoke Test:
- e2e/smoke.spec.ts: Navigate to / and assert page title
- Verifies Next.js app loads successfully

Package Updates:
- Added @playwright/test@^1.58.2
- Added test:e2e script to run Playwright tests
- Chromium browser (v1208) installed

Note: Vitest setup was completed in Task 10
Build: TypeScript checks pass, 1 test discovered
Pattern: Standard Playwright configuration for Next.js

frontend/package.json

@@ -8,7 +8,8 @@
     "start": "next start",
     "lint": "eslint",
     "test": "vitest run",
-    "test:watch": "vitest"
+    "test:watch": "vitest",
+    "test:e2e": "playwright test"
   },
   "dependencies": {
     "@auth/core": "^0.34.3",
@@ -25,6 +26,7 @@
     "tailwind-merge": "^3.5.0"
   },
   "devDependencies": {
+    "@playwright/test": "^1.58.2",
     "@tailwindcss/postcss": "^4",
     "@testing-library/jest-dom": "^6.9.1",
     "@testing-library/react": "^16.3.2",