Errors: refuse links the probe can't play (with Put it up anyway), plain error texts, and others see who can't play

report.error / state.members[].error (optional, no protocol bump): an
errored member is out of the ready gate until its player opens the media
or the media changes; others see "Bob can't play this: ..." and a mark
on the avatar; your own pill offers Retry (reload).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/desktop/lib/src/sync/sync_client.dart

@@ -219,6 +219,7 @@ class SyncClient {
     double duration = 0,
     int mediaId = 0,
     Map<String, bool>? jf,
+    String error = '',
   }) {
     final safeBuffered = buffered.isNaN || buffered < 0 ? 0.0 : buffered;
     _send(
@@ -229,6 +230,7 @@ class SyncClient {
         duration: duration.isFinite && duration > 0 ? duration : 0,
         mediaId: mediaId,
         jf: jf,
+        error: error,
       ).toJson(),
     );
   }