fix: ESC in immersive now exits fullscreen too (#202)

ESC key was calling onClose() directly, skipping the fullscreen
exit logic. Changed to handleExitImmersive() which exits fullscreen
before closing, matching the behavior of the UI close buttons.

cc

src/lib/components/immersive/ImmersivePlayer.svelte

@@ -282,7 +282,7 @@
 
     switch (e.key) {
       case 'Escape':
-        onClose();
+        handleExitImmersive();
         break;
       case 'F11':
         e.preventDefault();