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/layout/activity_server_setup.xml

@@ -88,6 +88,27 @@
 
             </com.google.android.material.textfield.TextInputLayout>
 
+            <!-- QR Code Scan Button -->
+            <Button
+                android:id="@+id/scanQrButton"
+                style="?attr/materialButtonOutlinedStyle"
+                android:layout_width="match_parent"
+                android:layout_height="wrap_content"
+                android:layout_marginTop="24dp"
+                android:text="@string/scan_qr_code_button"
+                android:drawableLeft="@drawable/ic_qr_scan"
+                android:drawablePadding="8dp"
+                android:paddingVertical="12dp" />
+
+            <TextView
+                android:layout_width="match_parent"
+                android:layout_height="wrap_content"
+                android:layout_marginTop="8dp"
+                android:text="@string/scan_qr_code_hint"
+                android:textAlignment="center"
+                android:textSize="12sp"
+                android:textStyle="italic" />
+
             <TextView
                 android:id="@+id/testConnectionInfo"
                 android:layout_width="match_parent"

app/src/main/res/layout/activity_settings.xml

@@ -67,6 +67,18 @@
                 android:inputType="textPassword" />
         </com.google.android.material.textfield.TextInputLayout>
 
+        <!-- QR Code Scan Button -->
+        <Button
+            android:id="@+id/scanQrButton"
+            style="?attr/materialButtonOutlinedStyle"
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            android:layout_marginTop="16dp"
+            android:layout_marginBottom="8dp"
+            android:text="@string/scan_qr_code_button"
+            android:drawableLeft="@drawable/ic_qr_scan"
+            android:drawablePadding="8dp" />
+
         <Button
             android:id="@+id/saveSettingsButton"
             android:layout_width="match_parent"