Art(engine): ArtStaging style-proof scene + first baked statics

Assets/Scenes/ArtStaging.unity — murk env + warm-key/cold-gloam lights +
game-angle camera + bloom/ACES post volume + pedestal + SLOT markers.
Baked statics (glTFast): SM_Prop_CargoCrate (shared M_Lit_Palette) +
SM_Prop_GlowFlora (palette stalks + HDR-teal emissive bulbs -> blooms).
Validates the palette pipeline + Emissive-Gloam bloom in URP.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

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