fix(topbar): announce the output stage when recording starts or stops

Starting a local recording left the idle 'Start Recording' chip on screen and never revealed 'Stop
Recording' — IsRecording raised its own notifications but not the output stage's, so the visibility
bindings were never re-evaluated. The visible chip's command then correctly refused to run (recording was
already in progress), which is the worst shape of bug: a dead button that looks live.

IsRecording and StreamStatus now call RaiseOutputStage(). The regression test asserts the NOTIFICATIONS,
not the property values — reading ShowEndRecordingAction directly passes either way, which is exactly how
this slipped through.

682 pass, 0 warnings.

ViewModels/MainViewModel.Streaming.cs

@@ -87,6 +87,7 @@ public partial class MainViewModel : ViewModelBase
                 OnPropertyChanged(nameof(ShowChatInactiveMessage));
                 OnPropertyChanged(nameof(ShowPreviewPlaceholder));
                 RaiseTopBarModes();
+                RaiseOutputStage();     // IsLive drives ShowOutputStage
                 UpdateLiveVisuals();
             }
         }
@@ -170,6 +171,7 @@ public partial class MainViewModel : ViewModelBase
             OnPropertyChanged(nameof(EndButtonText));
             OnPropertyChanged(nameof(ShowTestButton));
             RaiseTopBarModes();
+            RaiseOutputStage();         // Start Recording <-> Stop Recording, and the REC clock
             UpdateSessionTimer();
         }
     }