Add Capacitor Android project and native Tiptoi plugin

Checked-in android/ Capacitor project plus the native TiptoiPlugin
(Kotlin): SAF directory picker for the pen, listing/copying/deleting
.gme files on the pen, and downloading GME/cover files into
app-private storage.

client/capacitor.config.ts

@@ -0,0 +1,19 @@
+import type { CapacitorConfig } from '@capacitor/cli'
+
+// DEV_URL aktiviert den Capacitor Live-Reload gegen den Vite-Dev-Server.
+// Beispiel: DEV_URL=http://192.168.1.42:5173 bun run cap:android
+const devUrl = process.env.DEV_URL
+
+const config: CapacitorConfig = {
+  appId: 'com.tiptoisync.app',
+  appName: 'TipToi Sync',
+  webDir: 'dist',
+  server: devUrl
+    ? { url: devUrl, cleartext: true }
+    : { androidScheme: 'https' },
+  android: {
+    allowMixedContent: true,
+  },
+}
+
+export default config