Add ray_renderer to src/renderer for visualizing input rays and collision cursors

[yorkie]

Background

To enhance XR interaction and debugging, we need a dedicated renderer that can visualize rays (Ray) and collision cursors based on current input sources and the scene's depth buffer.

Proposal

• Implement a new ray_renderer module in src/renderer.
• The renderer should maintain multiple Rays, each representing an input/collision ray.
• For each frame, it should:
  • Fetch the currently active input sources.
  • Retrieve the target ray from each input source for collision detection.
  • Based on the ray and the current FBO's depth buffer, draw:
    • The rays (lines in 3D)
    • The collision cursor at the intersection point (with option to use a configurable cursor image)
• The ray_renderer should allow configuring the cursor image/appearance.

Technical Notes

• Integration with the input system is needed to pull updated target rays.
• Depth buffer readback should be considered (possibly via glReadPixels or shader-based raymarching if performance is a concern).
• The renderer should be able to support multiple simultaneous rays (e.g., for multi-controller/multi-hand scenarios).

Acceptance Criteria

• src/renderer/ray_renderer.* implements the above logic
• Can visualize rays and collision cursors in the XR scene
• Configurable cursor image/appearance
• Supports multiple input sources
• Hooked up to the main render loop for real-time updates

Related

• Input system (for input source & target ray)
• Depth buffer (for collision/cursor placement)

---

This will help with debugging and future user interaction features in JSAR.