feat: Add community management features with QR code scanning

- Implement Community model for managing community data, including secret handling and PSK derivation.
- Create CommunityQrScannerScreen for scanning and joining communities via QR codes.
- Develop CommunityStore for persisting community data using SharedPreferences.
- Introduce QrCodeDisplay widget for displaying QR codes with customizable options.
- Add QrScannerWidget for reusable QR code scanning functionality with validation and controls.

pubspec.yaml

@@ -53,6 +53,8 @@ dependencies:
   wakelock_plus: ^1.2.8
   characters: ^1.4.0
   package_info_plus: ^8.0.0
+  mobile_scanner: ^6.0.0  # QR/barcode scanning
+  qr_flutter: ^4.1.0      # QR code generation
 
 dev_dependencies:
   flutter_test:
@@ -78,6 +80,9 @@ flutter:
   # the material Icons class.
   uses-material-design: true
 
+  assets:
+    - assets/images/
+
 flutter_launcher_icons:
   android: true
   ios: true