Renderer: baked GI / lightmap path for static geometry

[drsnuggles8]

Problem

GI is realtime-only (SSGI + IBL). There's no baked lightmap / irradiance-volume path for static geometry. It looks fine, but you lose a major perf lever and ground-truth bounce lighting for static-heavy scenes.

Why it matters (Tier 3)

A baked path gives high-quality, cheap indirect lighting for the static world (terrain, buildings, props), freeing the realtime budget for dynamic objects. Standard for shipping open-world titles.

Proposed approach (compute/offline)

• Offline lightmap bake (UV2 unwrap + path-traced or irradiance bake — can run in compute) for static meshes; runtime samples the lightmap.
• And/or baked irradiance volumes (probe grid) for dynamic objects sitting in static lighting.
• The bake step lives in the asset-cook pipeline (AssetPackBuilder / BuildGamePanel).

Acceptance criteria

• A static scene shows baked indirect bounce; dynamic objects sample baked probes; runtime cost lower than full SSGI for the same look.

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Tier 3 — visual quality / perf lever.

Score

capability: 5
craft: 13
stability: 1
decay: 1
effort: 8
confidence: 0.5
learning: 5
fun: 5
kano: delighter
blocked_by: []
blocks: []

_{Rated per issue-scoring · score = confidence × (capability + craft + stability + decay) / effort, derived by the picker.}