perf: clash-detection broadphase + raster material tints

[ecto]

What

Three renderer/eval fixes found by tracing why a large imported document never finished rendering:

1. Clash detection broadphase (vcad-eval): evaluate_document ran a blind O(n²) pairwise BRep intersection across all scene roots. On a many-root document this dominates everything — an imported chip die (~88k roots, zero actual overlaps) sat at 84% of profile samples inside boolean_op/face_aabb and would effectively never finish (3.8 billion kernel booleans). Now: per-root AABBs computed once, sorted by min-x, sweep-and-prune — only genuinely overlapping boxes reach the kernel. AABB-disjoint pairs intersect to empty anyway, so results are identical.
2. vcad-render skips clash detection — a static renderer never displays clash meshes (the flag existed, nothing set it).
3. Raster path honors material tints (vcad-render --jpeg): render_jpeg_str silently dropped document material colors — hardcoded monochrome. Tinted parts now sample the same tinted shading ramp as the SVG path. Untinted parts keep the original shade byte-for-byte, and render_jpeg_solids stays monochrome, so mecheval reference images are unchanged.

Numbers

scenario	before	after
88k-root sky130 die (vcad-render)	never finishes	5.2 s
2,000 disjoint roots (evaluate_document)	minutes	0.23 s

Testing

• New clash_broadphase integration suite: overlap still detected (incl. same-x-extent pairs and root-order independence), disjoint scenes produce zero clashes, per-pair counts, and a 2,000-root wall-clock regression bound.
• cargo test -p vcad-eval -p vcad-render green; clippy -D warnings clean (incl. --all-features).

Found while importing a real OpenLane/sky130 GDS via #387 — the two PRs are independent but this one is what makes big imported layouts actually render.

🤖 Generated with Claude Code

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Project	Deployment	Actions	Updated (UTC)
vcad-mcp	Building	Preview, Comment	Jul 3, 2026 3:59am

3 Skipped Deployments

Project	Deployment	Actions	Updated (UTC)
mecheval	Ignored		Jul 3, 2026 3:59am
vcad	Ignored		Jul 3, 2026 3:59am
vcad-docs	Ignored		Jul 3, 2026 3:59am

[chojiai]

What shipped

This is an internal performance and correctness fix with no new user-facing features, but it resolves a real-world problem where large imported designs would never finish rendering.

• Documents with many components (such as large chip layouts) now render in seconds instead of hanging indefinitely.
• Parts with assigned material colors now appear correctly tinted in exported JPEG images, matching how they look in other views.

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