fix(#383): don't attribute room reactions to the room's own name

Adversarial review caught a data-loss defect in the reactor-name
fallback. For a reaction in a room from an author not in the local
contacts, _resolveContactSenderName returns null and the chain fell
through to reactionContact?.name. But reactionContact is the room server,
not the reactor, so every unknown-author reaction was attributed to the
room's display name. Two distinct unknown authors then both resolved to
that one name, so applyReaction's per-reactor dedup treated the second as
a duplicate and dropped it, count and all.

Fall back to the per-author hex (from the frame's own fourByteRoomContact
Key) instead, which is unique per reactor. In a true 1:1 that hex is
empty and the contact genuinely is the reactor, so its name stays the
correct fallback.

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

lib/connector/meshcore_connector.dart

@@ -6563,10 +6563,18 @@ class MeshCoreConnector extends ChangeNotifier {
       final reactingAuthorHex = message.fourByteRoomContactKey
           .map((b) => b.toRadixString(16).padLeft(2, '0'))
           .join();
+      // In a room, reactionContact is the room server, NOT the reactor, so its
+      // name must never be the fallback: it would attribute every unknown-author
+      // reaction to the room and then dedup distinct authors into one, dropping
+      // reactions (#383). Fall back to the per-author hex, which is unique per
+      // reactor. In a true 1:1 the author hex is empty and the contact IS the
+      // reactor, so its name is correct.
+      final fallbackName = (isRoomReaction && reactingAuthorHex.isNotEmpty)
+          ? reactingAuthorHex
+          : (reactionContact?.name ?? pubKeyHex);
       final reactorName =
           _resolveContactSenderName(message, reactionContact, isRoomReaction) ??
-          reactionContact?.name ??
-          (reactingAuthorHex.isNotEmpty ? reactingAuthorHex : pubKeyHex);
+          fallbackName;
       final reactionIdentifier =
           '${reactionInfo.targetHash}_${reactionInfo.emoji}_$reactingAuthorHex';