Player overlay: real transport buttons (pause/stop/audio), OK opens controls

OK now opens the overlay like every TV player; its buttons are ordinary
focusable pills (play/pause, stop, audio-track cycle). Back closes the
overlay first, then stops. Auto-hide timer restarts on any interaction.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

app/src/main/java/dev/castarr/tv/AppState.kt

@@ -42,6 +42,16 @@ class AppState(
         private set
     private var lastNowTitle: String? = null
 
+    /** Bumped on every interaction with the visible overlay to restart the
+     * auto-hide timer. */
+    var overlayPing by mutableLongStateOf(0L)
+        private set
+
+    fun pingOverlay() {
+        overlayVisible = true
+        overlayPing++
+    }
+
     /** Phone-first onboarding progress (ADR-0007). */
     var welcomePhase by mutableStateOf(WelcomePhase.WAIT_PHONE)
     var welcomeUserCode by mutableStateOf("")