Add QR code scanning for server configuration

Adds QR code scanning functionality to both ServerSetupActivity and
SettingsActivity, allowing users to auto-fill server configuration by
scanning a QR code from the server's admin dashboard.

Changes:
- Add ZXing Android Embedded library (v4.3.0) for QR scanning
- Add CAMERA permission to AndroidManifest
- Create QrServerConfig model to parse and validate QR JSON data
- Create QrScannerUtil for shared scanning functionality
- Extend PermissionUtil with camera permission handling
- Add "Scan QR Code" button to ServerSetupActivity with hint text
- Add "Scan QR Code" button to SettingsActivity
- Add QR scan icon and string resources
- Configure Gradle Java toolchain auto-detection

The QR code contains JSON with server address, port, and client key
which are automatically populated into the input fields when scanned.

app/src/main/AndroidManifest.xml

@@ -9,6 +9,7 @@
     <uses-permission android:name="android.permission.FOREGROUND_SERVICE" />
     <uses-permission android:name="android.permission.POST_NOTIFICATIONS" />
     <uses-permission android:name="android.permission.FOREGROUND_SERVICE_DATA_SYNC" />
+    <uses-permission android:name="android.permission.CAMERA" />
 
     <application
         android:allowBackup="false"