portrait-only: drop landscape rotate prompt + lock to portrait

- Remove RotatePrompt (the "rotate to landscape" overlay) — the app is portrait
  now, so it only blocked the UI.
- page.tsx: best-effort orientation lock switched landscape → portrait.
- Add Playwright-based store-screenshot + icon scripts (scripts/shots.js,
  game.js, icon.js); generated images are gitignored.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

package.json

@@ -35,6 +35,7 @@
     "@types/react-dom": "^19",
     "eslint": "^9",
     "eslint-config-next": "16.2.7",
+    "playwright": "^1.60.0",
     "tailwindcss": "^4",
     "typescript": "^5"
   }