HANDS: add realistic Boxer model and bounded arcade gore

[user1303836]

Summary

• replace the stylized Barbarian fighter with Texel, Inc.’s realistic rigged Boxer model under CC BY 4.0, with source attribution and modification notice
• retarget-bake the full 18-clip HANDS animation contract in a neutral root frame, preserve runtime facing, and validate every keyframe through CPU skin deformation, grounding, continuity, and live glove markers
• add bounded presentation-only arcade gore in full mode, including sprays, stains, gibs, fountains, and reversible decapitation proxies, while immediately clearing or suppressing graphic effects in reduced, off, and reduced-motion modes
• preserve the exact index.html / assets/hands.js / assets/hands.css deployment contract, await texture readiness, and strengthen bundle URL and size gates

Model source: https://sketchfab.com/3d-models/boxer-84767168720948b38728ff78ee6f6090

Validation

• uv run ruff check .
• uv run ruff format --check .
• uv run mypy src/
• uv run pytest tests/ — 1,891 passed
• npm run typecheck — passed
• npm run test:run — 185 passed
• npm run build / npm run scan:build — exact three-file manifest passed
• uv run python scripts/hands_replay.py --check — deterministic
• Khronos glTF Validator 2.0.0-dev.3.10 — 0 errors; 5 expected non-root skinned-mesh warnings
• deterministic fighter generation — 1,521,992-byte GLB, 18 clips, SHA-256 c26c87d11ff0eab83c1921e3ec4f352bbe05cd50b3b3916a7bda1962790d94e2
• browser captures reviewed for all 18 clips and full-mode decapitation; same-session SwiftShader regression remained below 10%

Bundle note

The required inline model and five textures increase hands.js to 5,624,575 bytes raw / 2,942,823 bytes at gzip level 9. Build and wheel checks enforce ceilings of 6,000,000 raw / 3,200,000 gzip bytes.

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