Upgrade XrNavigation teleport visuals to ballistic arc with ring indicator

Replaces the line-based teleport visualization with a modern, Quest-style
presentation, with no physics-engine dependency:

- Teleport aim is now a ballistic parabolic arc rendered as a glowing
  soft-edged ribbon mesh (camera-billboarded, alpha-faded edges/ends),
  with a shader-drawn glowing ring at the landing point
- Ground detection uses a configurable groundHeight plane (was hardcoded
  y=0), plus an optional castRay callback so apps with physics or custom
  picking can supply real ground detection; elevated hits step the rig
  up/down correctly
- Teleport commit and visualization share the same arc computation, so
  landings match the visual exactly (also fixes teleporting beyond
  maxTeleportDistance while the ray showed invalid)
- Aim originates from the grip position when available - the target ray
  origin sits at the head for gaze/pinch input (e.g. Apple Vision Pro)
- Shaders provided in GLSL and WGSL (WebGL2 + WebGPU)
- Holds a refcount on the shared ring mesh so transient input sources
  (one per pinch on visionOS) cannot destroy it on removal
- Removes the always-on white controller rays and the line-circle
  indicator; removes controllerRayColor and teleportIndicatorSegments
- Softer default colors (cyan-white valid, muted salmon invalid)
- Cleans up all event handlers, meshes and materials on script destroy

New attributes: groundHeight, teleportArcSpeed, arcWidth, arcSegments.
New property: castRay.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: willeastcott