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

overlay/tsconfig.json

@@ -0,0 +1,19 @@
+{
+  "compilerOptions": {
+    "sourceMap": true,
+    "jsx": "react",
+    "target": "ES2016",
+    "module": "ES2020",
+    "allowJs": true,
+    "strict": true,
+    "esModuleInterop": true,
+    "moduleResolution": "bundler",
+    "resolveJsonModule": true,
+    "outDir": "dist",
+    "rootDir": "./src",
+    "skipLibCheck": true,
+    "lib": ["ES2016", "DOM"]
+  },
+  "exclude": ["node_modules", "dist"],
+  "include": ["src"]
+}