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/res/values/strings.xml

@@ -67,4 +67,13 @@
     <string name="expiry_time_note">Maximum 24 hours (1 day)</string>
     <string name="cancel_button">Cancel</string>
     <string name="upload_button">Upload</string>
+
+    <!-- QR Code Scanning -->
+    <string name="scan_qr_code_button">Scan QR Code</string>
+    <string name="scan_qr_code_hint">Scan a QR code from your server admin panel to auto-fill settings</string>
+    <string name="qr_scan_success">Configuration loaded from QR code</string>
+    <string name="qr_scan_cancelled">QR code scan cancelled</string>
+    <string name="qr_scan_error">QR code error: %1$s</string>
+    <string name="camera_permission_required">Camera permission is required to scan QR codes</string>
+    <string name="camera_permission_denied">Camera permission denied. Please enable it in Settings to scan QR codes.</string>
 </resources>