feat(pcb): evaluate PcbBoard to a real centered FR4 solid in the live app

[ecto]

What

Makes a PCB board a genuine FR4 solid in the live app path (Task 1 from the modeless-PCB follow-up), not just a data-only placeholder rendered by a workaround.

The merged foundation (#227) added PcbBoard evaluation to vcad-eval and the TS evaluator, but the CRDT materializer still emitted CsgOp::Empty for a board node — so the live app never reached that code, and boards only appeared via the PcbBoardBodies data-mesh workaround (and were invisible in STEP export / ray tracing).

Changes

• crates/vcad-app/materializer.rs — emit a real PcbBoard op (mirroring the EmbroideryPattern case) so the kernel extrudes a genuine slab. doc.pcb is still set for the legacy getNodePcb fallback. (This is the change that actually activates the board solid in the app.)
• Centering in vcad-eval/evaluate.rs, vcad-kernel-wasm evaluate_node (the requested VCode-path arm, with cutouts noted TODO), and TS engine/evaluate.ts — the kernel extrudes from z=0, so shift the slab down by thickness/2. The top surface now lands at +thickness/2, exactly where PcbScene draws the copper (layerZ = thickness/2 + …) and where the legacy PcbBoardMesh sat.
• Reconcile the double-slab: ViewportContent renders <PcbScene showBoard={false} />, and PcbBoardBodies is gutted to only the doc.pcb-only legacy path. The kernel part is now the single source of the slab — no z-fighting/doubling, focused or not.
• data/materials.ts — resolve the board's __pcb_fr4__ material key to FR4 green (#0d5a2d); previously unresolved → board rendered default white.
• Test — vcad-eval unit test asserting a board evaluates to a non-empty solid centered on z=0 (also covers export-non-empty).
• Regenerated kernel WASM artifacts.

Verification

Built and run locally. Verified against the running app's actual Three.js scene + evaluated meshes:

• ✅ Board evaluates to a real solid — evaluated mesh non-empty; unit test green.
• ✅ Slab centered z ∈ [-0.8, 0.8] for a 1.6 mm board (was [0, 1.6]); matches the copper plane.
• ✅ Board mesh renders FR4 green — read the live material color: rgb(0.051, 0.353, 0.176) = #0d5a2d.
• ✅ Single board slab mesh in the scene (no z-fight) with PcbBoardBodies returning null for real PcbBoard nodes; the ghosted mechanical box stays at opacity 0.16.
• ✅ cargo test --workspace, npm test --workspaces, npm run build -w @vcad/app, and cargo clippy/cargo fmt on the changed crates all pass.

Note: the only cargo clippy --workspace -- -D warnings failures are pre-existing needless_borrow lints in the untouched vcad-desktop crate (newer clippy 1.95.0); my crates are clean. Framed 3D screenshots were unreliable in the headless preview (on-demand frameloop + transparent canvas), so the board appearance was verified by reading the rendered Three.js material/geometry directly rather than by pixel capture.

🤖 Generated with Claude Code

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4 Skipped Deployments

Project	Deployment	Actions	Updated (UTC)
mecheval	Ignored		Jun 3, 2026 9:06pm
vcad	Ignored		Jun 3, 2026 9:06pm
vcad-docs	Ignored		Jun 3, 2026 9:06pm
vcad-mcp	Ignored		Jun 3, 2026 9:06pm