Update three-debugging.md to reflect that the shadow intermittence
is resolved by explicit sun.shadow.needsUpdate = true at mount and
in useFrame after updateMatrixWorld.
- Drop SceneShadowWarmup section, document centralized shadow config.
- Document the localized Suspense boundaries in World.tsx.
- Document the new player model and octree debug visualizations.
- Open note about intermittent first-load shadow rendering.