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 <noreply@anthropic.com>
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 <noreply@anthropic.com>
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 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

---------

Co-authored-by: jyviko <2501648+jyviko@users.noreply.github.com>
Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

crates/mesh/src/lib.rs

@@ -7,6 +7,8 @@
 #![deny(clippy::unwrap_used, clippy::expect_used, clippy::panic, clippy::unimplemented, clippy::todo, clippy::unreachable)]
 #![forbid(unsafe_code)]
 
+pub mod quality;
+
 #[derive(Debug, Clone, PartialEq, thiserror::Error)]
 pub enum Error {
     #[error("invalid input: {0}")]