improve-threejs

# Three.js review Identify the affected scene, render loop, and requested outcome. For an audit, return evidence without edits; for an improvement request, fix verified problems within scope. Prioritize observed frame cost, GPU resource lifetime, and visible rendering defects. Read [scene review](references/scene-review.md) for frame-loop, disposal, camera/material, and visual checks relevant to the task. Use the installed React Doctor only when its diagnostics help; scores are not a target. Preserve deliberate animation and reduced-motion behavior. Verify a visual claim against a rendered frame or label it as a source inference. Browser work follows the shared session lock. Recheck affected interactions using comparable settings, and report measured outcomes and remaining limitations.