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

scripts/apply-overlay.mjs

@@ -0,0 +1,102 @@
+/**
+ * Applies mobile-specific overlay files from the overlay/ directory on top of the cinny submodule.
+ *
+ * This script:
+ *  1. Copies config.json (root) into cinny/config.json
+ *  2. Copies all source files from overlay/src/ into cinny/src/
+ *  3. Copies overlay/tsconfig.json into cinny/tsconfig.json
+ *  4. Merges overlay/package-additions.json dependencies into cinny/package.json
+ *  5. Copies capacitor.config.json (root) into cinny/capacitor.config.json with webDir reset to "dist"
+ *  6. Creates a Windows directory junction cinny/android -> root android/ so Capacitor can find it
+ *
+ * Run before every Android build to keep the cinny submodule clean while layering
+ * the Capacitor / Android platform changes on top of it.
+ */
+
+import { readFileSync, writeFileSync, mkdirSync, copyFileSync, readdirSync, statSync, existsSync } from 'fs';
+import { join, dirname, relative, resolve } from 'path';
+import { fileURLToPath } from 'url';
+import { execSync } from 'child_process';
+
+const __dirname = dirname(fileURLToPath(import.meta.url));
+const ROOT = join(__dirname, '..');
+const CINNY = join(ROOT, 'cinny');
+const OVERLAY = join(ROOT, 'overlay');
+
+/**
+ * Recursively copy all files from src directory to dest directory.
+ * @param {string} src
+ * @param {string} dest
+ */
+function copyDirRecursive(src, dest) {
+  mkdirSync(dest, { recursive: true });
+  for (const entry of readdirSync(src)) {
+    const srcPath = join(src, entry);
+    const destPath = join(dest, entry);
+    if (statSync(srcPath).isDirectory()) {
+      copyDirRecursive(srcPath, destPath);
+    } else {
+      copyFileSync(srcPath, destPath);
+      console.log(`  overlay: ${relative(ROOT, destPath)}`);
+    }
+  }
+}
+
+// 1. Copy config.json to cinny/config.json
+console.log('[apply-overlay] Copying config.json...');
+copyFileSync(join(ROOT, 'config.json'), join(CINNY, 'config.json'));
+console.log(`  copied config.json -> cinny/config.json`);
+
+// 2. Copy overlay source files into cinny/src/
+console.log('[apply-overlay] Copying source files...');
+copyDirRecursive(join(OVERLAY, 'src'), join(CINNY, 'src'));
+
+// 3. Copy tsconfig.json
+console.log('[apply-overlay] Copying tsconfig.json...');
+copyFileSync(join(OVERLAY, 'tsconfig.json'), join(CINNY, 'tsconfig.json'));
+console.log(`  overlay: cinny/tsconfig.json`);
+
+// 4. Merge package-additions.json into cinny/package.json
+console.log('[apply-overlay] Merging package dependencies...');
+const cinnyPkg = JSON.parse(readFileSync(join(CINNY, 'package.json'), 'utf8'));
+const additions = JSON.parse(readFileSync(join(OVERLAY, 'package-additions.json'), 'utf8'));
+
+cinnyPkg.dependencies = {
+  ...cinnyPkg.dependencies,
+  ...(additions.dependencies ?? {}),
+};
+if (additions.devDependencies) {
+  cinnyPkg.devDependencies = {
+    ...cinnyPkg.devDependencies,
+    ...additions.devDependencies,
+  };
+}
+
+writeFileSync(join(CINNY, 'package.json'), JSON.stringify(cinnyPkg, null, 2) + '\n', 'utf8');
+console.log(`  merged ${Object.keys(additions.dependencies ?? {}).length} dep(s) into cinny/package.json`);
+
+// 5. Copy capacitor.config.json to cinny/ with webDir corrected back to "dist"
+console.log('[apply-overlay] Writing cinny/capacitor.config.json...');
+const rootCapConfig = JSON.parse(readFileSync(join(ROOT, 'capacitor.config.json'), 'utf8'));
+const cinnyCapConfig = { ...rootCapConfig, webDir: 'dist' };
+writeFileSync(join(CINNY, 'capacitor.config.json'), JSON.stringify(cinnyCapConfig, null, 2) + '\n', 'utf8');
+console.log(`  wrote cinny/capacitor.config.json (webDir: "dist")`);
+
+// 6. Create a directory junction cinny/android -> root android/ so Capacitor CLI can find it
+console.log('[apply-overlay] Setting up android/ junction...');
+const androidJunction = join(CINNY, 'android');
+const androidTarget = resolve(ROOT, 'android');
+if (!existsSync(androidJunction)) {
+  try {
+    execSync(`cmd /c mklink /J "${androidJunction}" "${androidTarget}"`, { stdio: 'pipe' });
+    console.log(`  created junction: cinny/android -> ${androidTarget}`);
+  } catch (err) {
+    console.warn('  mklink /J failed, falling back to directory copy...');
+    copyDirRecursive(androidTarget, androidJunction);
+    console.log(`  copied android/ into cinny/android/`);
+  }
+} else {
+  console.log(`  android/ junction already exists, skipping`);
+}
+
+console.log('[apply-overlay] Done.');