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/playwright.config.ts

@@ -0,0 +1,28 @@
+import { defineConfig, devices } from '@playwright/test';
+
+export default defineConfig({
+  testDir: './e2e',
+  fullyParallel: true,
+  forbidOnly: !!process.env.CI,
+  retries: process.env.CI ? 2 : 0,
+  workers: process.env.CI ? 1 : undefined,
+  reporter: 'html',
+  use: {
+    baseURL: 'http://localhost:3000',
+    screenshot: 'only-on-failure',
+    trace: 'on-first-retry',
+  },
+
+  projects: [
+    {
+      name: 'chromium',
+      use: { ...devices['Desktop Chrome'] },
+    },
+  ],
+
+  webServer: {
+    command: 'bun dev',
+    url: 'http://localhost:3000',
+    reuseExistingServer: !process.env.CI,
+  },
+});