feat: add Codec2 voice messages over LoRa mesh (iOS/macOS only)

Push-to-talk voice messaging using the Codec2 ultra-low-bitrate speech
codec, transmitted as V: prefixed packets over the existing MeshCore
LoRa mesh pipeline.

Voice recording UI (long-press send button or + menu) is gated behind
Platform.isIOS || Platform.isMacOS since the `record` package only
supports microphone capture on those platforms in this build.

Key changes:
- VoiceRecorderService: streams 8kHz mono PCM chunks via `record` package
- VoicePlayerService: decodes Codec2 bytes to WAV and plays via audioplayers
- VoiceCodecService: async Codec2 encode/decode in background isolates
- VoiceProvider: reassembles multi-packet sessions, drives playback
- VoiceMessageBubble: shows packet progress, play/stop controls
- MessagesProvider: detects V: prefix, routes to VoiceProvider
- MessagesTab: PTT long-press gesture + recording indicator (iOS/macOS)
- Message model: isVoice + voiceId fields for session tracking
- Auto-selects codec mode from radio bandwidth (700C/1200/1300 bps)
- codec2_flutter + meshcore_client switched from path to git deps

lib/providers/connection_provider.dart

@@ -167,6 +167,7 @@ class ConnectionProvider with ChangeNotifier {
   Function(String messageId, int echoCount, int snrRaw, int rssiDbm)?
   onMessageEchoDetected;
   Function(Uint8List publicKeyPrefix, Uint8List statusData)? onStatusResponse;
+  Function(Uint8List payload, int snrRaw, int rssiDbm)? onRawDataReceived;
 
   // Track pending send operations for auto-recovery
   final Map<String, _PendingSendOperation> _pendingSendOperations = {};
@@ -498,6 +499,10 @@ class ConnectionProvider with ChangeNotifier {
       onStatusResponse?.call(publicKeyPrefix, statusData);
     };
 
+    _bleService.onRawDataReceived = (payload, snrRaw, rssiDbm) {
+      onRawDataReceived?.call(payload, snrRaw, rssiDbm);
+    };
+
     _bleService.onDeviceInfoReceived = (deviceInfo) {
       debugPrint('📥 [Provider] Received DeviceInfo:');
       debugPrint('  Firmware Version: ${deviceInfo['firmwareVersion']}');
@@ -1318,6 +1323,21 @@ class ConnectionProvider with ChangeNotifier {
     }
   }
 
+  /// Send a raw binary voice packet directly to a contact (cmdSendRawData, code 25).
+  /// Only works for contacts with a known direct route (outPathLen >= 0).
+  Future<void> sendRawVoicePacket({
+    required Uint8List contactPath,
+    required int contactPathLen,
+    required Uint8List payload,
+  }) async {
+    if (!_bleService.isConnected) return;
+    await _bleService.sendRawVoicePacket(
+      contactPathLen: contactPathLen,
+      contactPath: contactPath,
+      payload: payload,
+    );
+  }
+
   /// Request telemetry from contact
   ///
   /// COMPATIBILITY NOTE: This method sends CMD_SEND_TELEMETRY_REQ (39).