Initial commit: MeshCore Open Flutter client

Open-source Flutter client for MeshCore LoRa mesh networking devices.

Features:
- BLE device scanning and connection
- Nordic UART Service (NUS) integration
- Material 3 design with system theme support
- Provider-based state management
- Placeholder screens for chat, contacts, and settings

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

lib/models/contact_group.dart

@@ -0,0 +1,37 @@
+class ContactGroup {
+  final String name;
+  final List<String> memberKeys;
+
+  const ContactGroup({
+    required this.name,
+    required this.memberKeys,
+  });
+
+  ContactGroup copyWith({
+    String? name,
+    List<String>? memberKeys,
+  }) {
+    return ContactGroup(
+      name: name ?? this.name,
+      memberKeys: memberKeys ?? List<String>.from(this.memberKeys),
+    );
+  }
+
+  Map<String, dynamic> toJson() {
+    return {
+      'name': name,
+      'members': memberKeys,
+    };
+  }
+
+  factory ContactGroup.fromJson(Map<String, dynamic> json) {
+    final members = (json['members'] as List?)
+            ?.map((value) => value.toString())
+            .toList() ??
+        <String>[];
+    return ContactGroup(
+      name: json['name'] as String? ?? '',
+      memberKeys: members,
+    );
+  }
+}