feat: Implement optimized contact fetching by public key to enhance performance

lib/services/meshcore_ble_service.dart

@@ -311,6 +311,20 @@ class MeshCoreBleService {
     await _commandSender.writeData(FrameBuilder.buildGetContacts());
   }
 
+  /// Get a single contact by public key from device
+  ///
+  /// This is more efficient than getContacts() when you only need to refresh
+  /// one specific contact (e.g., after receiving an advertisement).
+  ///
+  /// The contact will be delivered via the onContactReceived callback.
+  Future<void> getContactByKey(Uint8List publicKey) async {
+    debugPrint('🔍 [BLE] Requesting single contact by key:');
+    debugPrint(
+      '    Public key prefix: ${publicKey.sublist(0, 6).map((b) => b.toRadixString(16).padLeft(2, '0')).join(':')}...',
+    );
+    await _commandSender.writeData(FrameBuilder.buildGetContactByKey(publicKey));
+  }
+
   /// Manually add or update a contact on the companion radio
   Future<void> addOrUpdateContact(Contact contact) async {
     debugPrint('📝 [BLE] Adding/updating contact on companion radio:');

lib/services/meshcore_constants.dart

@@ -39,6 +39,7 @@ class MeshCoreConstants {
   static const int cmdSendRawData = 25;
   static const int cmdSendLogin = 26;
   static const int cmdSendStatusReq = 27;
+  static const int cmdGetContactByKey = 30;
   static const int cmdGetChannel = 31;
   static const int cmdSetChannel = 32;
   static const int cmdSignStart = 33;

lib/services/meshcore_opcode_names.dart

@@ -59,6 +59,8 @@ class MeshCoreOpcodeNames {
         return 'SEND_LOGIN';
       case MeshCoreConstants.cmdSendStatusReq:
         return 'SEND_STATUS_REQ';
+      case MeshCoreConstants.cmdGetContactByKey:
+        return 'GET_CONTACT_BY_KEY';
       case MeshCoreConstants.cmdGetChannel:
         return 'GET_CHANNEL';
       case MeshCoreConstants.cmdSetChannel:

lib/services/protocol/frame_builder.dart

@@ -31,6 +31,14 @@ class FrameBuilder {
     return writer.toBytes();
   }
 
+  /// Build GetContactByKey command - retrieves a single contact by public key
+  static Uint8List buildGetContactByKey(Uint8List publicKey) {
+    final writer = BufferWriter();
+    writer.writeByte(MeshCoreConstants.cmdGetContactByKey); // 0x1E (30)
+    writer.writeBytes(publicKey); // 32 bytes
+    return writer.toBytes();
+  }
+
   /// Build AddUpdateContact command
   static Uint8List buildAddUpdateContact(Contact contact) {
     final writer = BufferWriter();