test: add Playwright smoke suite (cookie banner, lang switcher, FamilyAtlas, WritingIssue)

34 tests across desktop + mobile (Chromium/Pixel 5). Verifies all client-side
React islands and interactive features that astro build/WebFetch cannot confirm.
API-dependent WritingIssue shows graceful error against local preview; resolves
on the live site where the PHP backend is available.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

package.json

@@ -12,7 +12,8 @@
     "build": "astro build",
     "preview": "astro preview",
     "astro": "astro",
-    "og": "node scripts/generate-og-images.mjs"
+    "og": "node scripts/generate-og-images.mjs",
+    "test": "playwright test"
   },
   "dependencies": {
     "@astrojs/react": "^5.0.2",
@@ -23,6 +24,7 @@
     "react-dom": "^19.2.4"
   },
   "devDependencies": {
+    "@playwright/test": "^1.60.0",
     "@resvg/resvg-js": "^2.6.2",
     "satori": "^0.26.0"
   }