rendering: local reflection probes (baked cubemap specular for interiors)

[shadow-kernel]

Context

Environment reflection is currently a sky/ground-color sphere approximation in standard.hlsl — every metallic or glossy PBR surface inside a windowless horror interior reflects the outdoor sky, which reads as deeply wrong in dark rooms. SSR is deferred to backlog by design; baked local cubemap probes are the standard cheap indoor fix and have no ticket anywhere.

Goal

ReflectionProbe component: bake a cubemap at the probe position in-editor, store it with the scene, and sample the nearest/blended probe for specular IBL instead of the sky approximation.

Acceptance Criteria

• ReflectionProbe component with box extents + bake button (renders 6 faces offscreen, prefilters mips by roughness)
• Probe cubemaps serialized with the scene and shipped in .vpak
• standard.hlsl samples the probe (box-projected) for specular IBL; falls back to sky when no probe covers the pixel
• Blending between overlapping probes or nearest-probe selection (documented choice)
• Dark-interior test scene: metallic props reflect the room, not the sky (before/after captures)

Technical Notes

Reuse AssetPreviewRenderer-style offscreen rendering for the bake; prefilter with a compute or pixel-shader mip chain (GGX importance sampling).

Dependencies

• rendering: post-processing framework (offscreen infrastructure, soft)