fix(security): properly cleanup MediaStream on camera access failure

- Add stopStreamTracks() call in catch block to release any partially
  acquired media tracks when camera access fails
- Prevents privacy and resource leaks from orphaned media streams

src/renderer/extensions/vueNodes/widgets/components/WidgetWebcam.vue

@@ -634,8 +634,8 @@ async function startCameraPreview() {
       )
     }
 
+    stopStreamTracks()
     isShowingPreview.value = false
-    isCameraOn.value = false
   }
 }