feat: add Android/Capacitor platform support via overlay system

- Add Android project (Capacitor-generated, app ID com.paarrot.app)
- Add capacitor.config.json at repo root (webDir: cinny/dist)
- Add overlay/ directory with mobile-specific source patches:
  - tauri.ts: Capacitor native detection, LocalNotifications, permission APIs
  - matrix.ts / useAuthenticatedMediaUrl.ts: legacy /_matrix/media/ URL support
  - SystemNotification.tsx: Capacitor permission request flow
  - ClientNonUIFeatures.tsx: Capacitor notification routing
  - tsconfig.json: moduleResolution bundler, rootDir set
  - package-additions.json: @capacitor/* deps to merge at build time
- Add scripts/apply-overlay.mjs: applies overlay onto clean cinny submodule before build
- Update android:prepare script to run apply-overlay before build + cap sync

package.json

@@ -6,7 +6,7 @@
     "node": ">=18.0.0"
   },
   "scripts": {
-    "android:prepare": "node -e \"require('fs').copyFileSync('config.json', 'cinny/config.json')\" && cd cinny && npm run build && npx cap sync android",
+    "android:prepare": "node scripts/apply-overlay.mjs && cd cinny && npm install && npm run build && npx cap sync android",
     "android:open": "cd cinny && npx cap open android",
     "android:run": "cd cinny && npx cap run android",
     "android:apk": "npm run android:prepare && cd cinny/android && gradlew.bat assembleDebug",