integration: add Playwright, axe and Lighthouse CI gates

Lock SEO, accessibility and crawlability with headless browser checks so regressions fail before a merge instead of after publication.

Co-authored-by: Cursor <cursoragent@cursor.com>

playwright.config.ts

@@ -0,0 +1,40 @@
+import { defineConfig, devices } from '@playwright/test';
+
+export default defineConfig({
+  testDir: './e2e',
+  testMatch: '**/*.e2e.ts',
+  forbidOnly: !!process.env['CI'],
+  retries: 0,
+  workers: 1,
+  reporter: [['list'], ['html', { open: 'never' }]],
+  use: {
+    baseURL: 'http://127.0.0.1:4173',
+    screenshot: 'only-on-failure',
+    trace: 'retain-on-failure',
+  },
+  webServer: {
+    command: 'npm run build && npm run serve:ssr',
+    url: 'http://127.0.0.1:4173',
+    env: { PORT: '4173' },
+    timeout: 300_000,
+    reuseExistingServer: !process.env['CI'],
+  },
+  projects: [
+    {
+      name: 'desktop',
+      use: {
+        ...devices['Desktop Chrome'],
+        viewport: { width: 1440, height: 900 },
+      },
+    },
+    {
+      name: 'mobile',
+      use: {
+        ...devices['Desktop Chrome'],
+        viewport: { width: 390, height: 844 },
+        hasTouch: true,
+        isMobile: true,
+      },
+    },
+  ],
+});