Open menu naturally via chapter events; M returns to menu; debounce M

The menu state machine advances from the menu-intro state to the menu state
only when the menu video crosses its chapter-2 marker (onChapter). Fire
onChapter from the video loop as PTS crosses playlist markers. Also route the
M key through the onMenu dispatcher so it returns to the menu video/title
(not just drawing menu items), and debounce the key against auto-repeat.

ui/src/main/java/dev/quoije/umd/ui/PlayerApp.java

@@ -69,8 +69,8 @@ public final class PlayerApp extends Application {
     private volatile boolean skipRequested = false;
 
     private volatile VsmxInterpreter menuInterpreter;
-    private volatile VsmxBaseObject mmActivate;
     private volatile VsmxNativeObject controllerObject;
+    private long lastMenuKeyNanos = 0;
 
     @Override
     public void start(Stage stage) {
@@ -147,12 +147,18 @@ public final class PlayerApp extends Application {
     }
 
     private void openMenuDirectly() {
+        // Debounce key auto-repeat.
+        long now = System.nanoTime();
+        if (now - lastMenuKeyNanos < 250_000_000L) {
+            return;
+        }
+        lastMenuKeyNanos = now;
+
         VsmxInterpreter interpreter = menuInterpreter;
         VsmxNativeObject c = controllerObject;
         if (interpreter != null && c != null) {
             VsmxBaseObject callback = c.getPropertyValue("onMenu");
             if (callback instanceof VsmxFunction function) {
-                System.err.println("[debug] returning to menu");
                 interpreter.interpretFunction(function, null, new VsmxBaseObject[0]);
             }
         }
@@ -212,7 +218,6 @@ public final class PlayerApp extends Application {
             controller = (Controller) controllerObject.getObject();
             moviePlayer = (MoviePlayer) movieplayer.getObject();
             menuInterpreter = interpreter;
-            mmActivate = globals.getPropertyValue("mm_activate");
             this.controllerObject = controllerObject;
             controller.callCallback(interpreter, "onAutoPlay", null);
         } catch (Exception e) {