Element quality metrics and the certified validity gate (mesh.quality) (#12)

* mesh: element quality metrics and a certified Jacobian validity check

Bernstein-form Jacobian determinants for tet4/tet10/wedge6/hex8/hex20, certified
by bounds and subdivision (Johnen-Remacle-Geuzaine 2013); Shewchuk 2002 tet
metrics, Knupp 2001 hex/wedge/quad metrics; quality report and the validity
gate meshers run on their output.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

* engine: mesh.quality command; model documents its node order

mesh.quality reports certified validity, volume and per-metric statistics with
fixed-range histograms. The model's ElementKind doc states the Abaqus/VTK node
order and that deck code reorders formats like Nastran CHEXA20.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

* quality: simplify after review; exact orient3d for tet4; gate on raw mesher arrays

- tet4 validity from the exact orient3d of the input coordinates
- validity_gate_elements takes (label, kind, coordinates) straight from a mesher
- one Jacobian per solid; certify caches piece bounds; product weights precomputed
- model::check_coordinates shared by set_node and quality; ElementKind is Ord
- engine: shared labels() parameter parser

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

---------

Co-authored-by: jyviko <[email protected]>
Co-authored-by: Claude Opus 5.5 <[email protected]>

ROADMAP.md

@@ -6,7 +6,7 @@ LS-PrePost, with hexahedral meshing as the centre of gravity, plus its own linea
 | Milestone | Scope | Status |
 |---|---|---|
 | M0 Foundation | Workspace, quality gates (`cargo xtask ci`), FE model, command engine with rollback and panic guard, CLI, geometry boundary on SolidCraft's kernel and tessellator | done |
-| M1 Surface preparation | Geometry in: open `.solidcraft` designs, rebuilt by SolidCraft, with persistent face names (done); face-tagged 3MF files (`geometry.import.mesh`, docs/formats/tagged-mesh.md, done); exact predicates (Shewchuk adaptive, symbolic perturbation, indirect LPI/TPI, done); weld, closed/manifold/orientation checks and feature edges on the tessellated boundary; mesh quality metrics | in progress |
+| M1 Surface preparation | Geometry in: open `.solidcraft` designs, rebuilt by SolidCraft, with persistent face names (done); face-tagged 3MF files (`geometry.import.mesh`, docs/formats/tagged-mesh.md, done); exact predicates (Shewchuk adaptive, symbolic perturbation, indirect LPI/TPI, done); weld, closed/manifold/orientation checks and feature edges on the tessellated boundary; mesh quality metrics and the certified validity gate (`modelcraft-mesh::quality`, `mesh.quality`, done) | in progress |
 | M2 Tetrahedral meshing | Bowyer–Watson Delaunay, robust constrained Delaunay boundary recovery (Diazzi et al. 2023), Delaunay refinement to a size field, ODT smoothing, Klingner–Shewchuk sliver removal; linear and quadratic tets | planned |
 | M3 Hexahedral meshing (core) | Octree/grid dual all-hex (valid on any input), then hex-dominant by tet recombination, then polycube for blocky parts; see docs/meshing/literature.md | planned |
 | M4 Model definition | Materials, sections, sets and surfaces, boundary conditions, loads, steps, output requests | planned |