Mirror a radio from another computer's broadcast data

Listen for Radio broadcast data from another Nonemm or N1MM computer and
record its frequency, mode and split as this computer's own radio. No
radio is controlled. The settings are in the Configure Radios dialog.

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

src/Nonemm.App/AppSession.cs

@@ -1018,6 +1018,7 @@ public sealed partial class AppSession : IDisposable
         announcing?.Stop();
         broadcasting?.Stop();
         data?.Dispose();
+        mirror?.Dispose();
         network?.Dispose();
         link?.Dispose();
         alternating?.Dispose();