Prompt for microphone permission when recording video in new camera.

Previously, the new camera would silently record video without audio
when microphone permission was missing. Now it shows the same rationale
dialog and permanent denial flow as the old camera.

demo/camera/src/main/java/org/signal/camera/demo/screens/main/MainScreen.kt

@@ -147,6 +147,9 @@ fun MainScreen(
                 is StandardCameraHudEvents.MediaSelectionClick -> {
                   // Doesn't need to be handled
                 }
+                is StandardCameraHudEvents.AudioPermissionRequired -> {
+                  // Doesn't need to be handled
+                }
               }
             }
           )