fix(#22): BLE notify-stream onError + await reaction-path send

BLE onValueReceived.listen had no onError, while USB (L1557) and TCP (L1669) both attach one that logs and gracefully disconnects; an error emission on the BLE notify stream was unhandled. Add a matching onError. Also await sendMessageWithRetry in the reaction branch of sendMessage -- the normal path already awaits it; the reaction path's unawaited call swallowed failures, contradicting its own 'same as normal messages' comment.

Verified, not assumed: Gemini's 'disconnect() not try-caught' was a FALSE POSITIVE (already wrapped at L2484-2489); 'deleteAllPaths silent void' is a sync in-memory clear (no async failure path). flutter analyze clean; Gemini-reviewed with no critique of these two changes.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

lib/connector/meshcore_connector.dart

@@ -2052,6 +2052,10 @@ class MeshCoreConnector extends ChangeNotifier {
       }
       _notifySubscription = _txCharacteristic!.onValueReceived.listen(
         _handleFrame,
+        onError: (error, stackTrace) {
+          _appDebugLogService?.error('BLE transport error: $error', tag: 'BLE');
+          unawaited(disconnect(manual: false));
+        },
       );
 
       _setState(MeshCoreConnectionState.connected);
@@ -2823,7 +2827,7 @@ class MeshCoreConnector extends ChangeNotifier {
       // Route through retry service (same as normal messages)
       // Don't use auto-rotation for reactions — just send directly
       if (_retryService != null) {
-        _retryService!.sendMessageWithRetry(contact: contact, text: text);
+        await _retryService!.sendMessageWithRetry(contact: contact, text: text);
       } else {
         final outboundText = prepareContactOutboundText(contact, text);
         await sendFrame(buildSendTextMsgFrame(contact.publicKey, outboundText));