Move the first-person walkthrough into @pascal-app/viewer (BVHEcctrl +
GlbWalkthroughController) and round out the GLB-consuming viewer:
- Walkthrough: fallback ground only on level 0 (upper floors rely on baked
slabs), hidden spawn marker, auto pointer-lock on enter, single-Esc exit via
pointerlockchange, force perspective on enter / restore on exit.
- GlbScene: monochrome strips baked textures and recolours meshes by surface
role using the active theme's clay tints; spawn node hidden from render.
- glb-export: camera/label/spawn identity extras for the viewer.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
