Keep the controllers in VR games while the screens stay up

Visible screens kept SteamVR's laser mouse on, which takes the controllers
away from a VR game. Now, by default, that's off while a scene app runs:
the screens stay over the game and the 3D mouse or the dashboard works
them. Frametop Display Settings has the choice (always, except during VR
games, only with the dashboard open); the socket command is controllers.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

display-settings/ft_display_settings.py

@@ -363,6 +363,8 @@ class Backend(QObject):
                 self._ask_screens(f"visibility {value}")
             elif key == "wrist_angle":
                 self._ask_screens(f"wrist {float(value):.1f}")
+            elif key == "controllers":
+                self._ask_screens(f"controllers {value}")
             else:
                 self._ask_screens(f"gesture {v['gesture_hand']} {float(v['gesture_angle']):.1f}")