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

android/app/src/main/res/drawable/ic_stat_paarrot.xml

@@ -0,0 +1,16 @@
+<?xml version="1.0" encoding="utf-8"?>
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="24dp"
+    android:height="24dp"
+    android:viewportWidth="24"
+    android:viewportHeight="24">
+    <path
+        android:fillColor="#FFFFFFFF"
+        android:pathData="M2,9.1C3.8,5.7 7.2,4 11.6,4c4.4,0 7.8,1.7 10.4,5.1l-2,1.6c-1.7,-1.5 -3.8,-2.4 -6.4,-2.7c-0.2,1.6 -1.6,2.9 -3.3,2.9c-1.7,0 -3.1,-1.2 -3.3,-2.8C5.1,8.5 3.5,9.1 2,10z" />
+    <path
+        android:fillColor="#FFFFFFFF"
+        android:pathData="M8.7,11.5c-2.8,0 -5.1,2.3 -5.1,5.1c0,3 2.4,5.4 5.5,5.4c2.9,0 5.4,-1.3 7,-3.7c-0.5,0.1 -0.9,0.2 -1.4,0.2c-3.5,0 -6.4,-2.8 -6.4,-6.3c0,-0.2 0,-0.4 0,-0.7z" />
+    <path
+        android:fillColor="#FFFFFFFF"
+        android:pathData="M14.7,12.3c3,0.1 5.3,1.6 7.3,4.2c-1.8,1.5 -4.1,2.4 -6.9,2.8c1,-1 1.6,-2.3 1.6,-3.8c0,-1.2 -0.3,-2.3 -0.9,-3.2z" />
+</vector>