[Noisemaker111]

Engine seam: packages/shell/src/render/materialAsset.tsx (adopts #2476)

Closes #259

What changed

• engine-ref.txt moves to engine beta 96fb073f (jgengine PR #2476). A model's variant level now skips a material selector its simplified asset dropped; the source level still throws on a selector that matches nothing.
• No harbor-heat/ source change. The cruiser's Paint 2 Carmine assignment is valid on the freshly pulled sports-car near and far GLTFs.

Cause and what is not confirmed

• The reported "matched no slots" error comes from per-level validation of materialAssignments in the engine. Before this bump, any level whose asset lacked the selected slot threw and took the whole entity down.
• Not reproduced here. With assets provisioned fresh (bun run provision harbor-heat), the old engine and this games beta both pass step 17. The asset state on the reporter's machine is unknown, so the engine change is the guard against the crash, not a proven fix for that machine.

Evidence

• bun run drive harbor-heat --game-dir <checkout>/harbor-heat --timeout 600 --steps harbor-heat/proofs/depth-session.json serving engine 96fb073f: 54 of 54 steps ok, 0 failed, wall 98 s.
• Engine test "a variant level whose simplification dropped a selected slot skips that selector, and the source level still throws": fails without the change, passes with it.
• check:engine-mode, check:engine-ref, check:capabilities, check:framework pass.