In-VR menu: replace chunky prop-knob panel with Godot Control UI in a SubViewport

WorldPanel is now the project's one SubViewport screen: MainMenu (tabs Player /
World / System; Return to spawn, Recalibrate body, Reset props, Ping, click
volume slider, scrollable log, FPS, Close) rendered by MenuScreen into a
960x640 SubViewport on a thin 0.36x0.24 m panel.

Input = touch-first hybrid cursor injected as mouse events: both controller
rays are projected analytically onto the panel plane, converted to viewport
pixels and pushed via Viewport.PushInput (MouseMotion/MouseButton, wheel from
thumbstick). Stylus tip within 6 cm = touch cursor (press crossing 0.6 cm from
the front, release past 1.8 cm); farther = laser cursor with trigger edge. One
owning hand per viewport. Haptic tick + synthesized click on press.

Kept: ax_button summon/dismiss, XROrigin3D parenting, grip drag (direct/laser)
with head re-orient, IsBlocking/IsPanelCollider. Locomotion's beam now takes
its length from WorldPanel.TryGetLaserDistance (no beam while touching) and
starts at the stylus tip. Recalibrate calls Recalibrate() on the first node in
group "calibration" (disabled when absent).

New headless regression scenes/menu_spike.tscn ("MENU: overall PASS").

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

scenes/menu_spike.tscn

@@ -0,0 +1,6 @@
+[gd_scene load_steps=2 format=3]
+
+[ext_resource type="Script" path="res://scripts/MenuSpike.cs" id="1_spike"]
+
+[node name="MenuSpike" type="Node3D"]
+script = ExtResource("1_spike")