feat(viewer): click-robot-to-teleop, Ctrl+click nav, overlay UX

- Click robot entity in 3D → engages teleop for that robot
  (WASD publishes to <robot>/cmd_vel). Click non-robot → disengages.
  Robot detection via entity path prefix matching (go2/g1/robot).

- Ctrl+click non-robot entity with position → nav goal
  (PointStamped LCM on /clicked_point). Plain click = Rerun selection.

- Overlay at (260,12), greyed out when disengaged with
  'click robot' hint. Bright when engaged, shows robot name.

- KeyboardHandler shared via Rc<RefCell<>> between DimosApp and
  on_event callback for robot selection state.

- Multi-robot infrastructure: set_active_robot() + set_engaged()
  for future per-robot channel switching.

Author: Ubuntu

Cargo.lock

@@ -3110,7 +3110,7 @@ dependencies = [
 
 [[package]]
 name = "dimos-viewer"
-version = "0.30.0-alpha.1+dev"
+version = "0.30.0-alpha.4"
 dependencies = [
  "bincode",
  "clap",