Planar all-quad meshing: size fields, TFI mapped meshes, free quad mesher (M5 base) (#18)

* Planar all-quad meshing: size fields, TFI mapped meshes, free quad mesher, planar quad validity

- modelcraft_mesh::size: SizeField trait, division counts, graded polyline division, per-loop parity
- modelcraft_mesh::quad: transfinite (Gordon-Hall) mapped meshes of four-sided regions; free
  all-quad meshes of polygons with holes on prescribed boundary nodes (half-resolution CDT with
  Ruppert refinement, Lee-Lo recombination, uniform split, smart Laplacian plus
  Freitag-Plassmann untangling), exact validity gate on every element
- modelcraft_mesh::quality: Robinson aspect ratio and skew for quads, exact planar quad validity

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

* quad mesher: true-boundary guard for Steiner points, untangling by corner area, parity retry, recombination quality floor; I-beam and perforated plate tests

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

* docs: quad meshing papers (B7), roadmap M5 and M2, architecture pipeline step

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

* quad mesher: simplify (shared corner and validity helpers, vertex rotation helper, guard decoupled from the CDT, verify inside the CDT, non-allocating final gate)

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

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

docs/architecture.md

@@ -68,7 +68,14 @@ Rules beyond the layer order:
    recombination (Pellerin et al. 2018), then polycube (DualCube labelling) for blocky parts;
    frame-field/integer-grid-map methods stay research. Validity uses a certified trilinear Jacobian
    check (Marschner et al. 2020), not corner Jacobians alone.
-5. **Quality.** Scaled Jacobian, aspect ratio, dihedral angles; every generated mesh is checked
+5. **Structured hex and face meshing.** Faces get all-quad meshes on shared, prescribed edge
+   nodes (`modelcraft-mesh::quad`): transfinite interpolation for four-sided faces (Gordon and
+   Hall 1973), and for free faces a half-resolution constrained Delaunay triangulation,
+   recombination (Lee and Lo 1994) and one uniform split that lands on the boundary nodes, then
+   smoothing and untangling; every quad is checked with exact predicates. One `SizeField` trait
+   (`modelcraft-mesh::size`) sets interior sizes and edge divisions, with even counts per loop.
+   Mapped and swept hex build on these face meshes.
+6. **Quality.** Scaled Jacobian, aspect ratio, dihedral angles; every generated mesh is checked
    for positive Jacobians and conserved volume before it reaches the model.
 
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