mesh: the tet objective sees needles; no tet below scaled Jacobian 0.3 on the skill's tet parts

The improvement objective was the smallest dihedral sine, which misses
needles: every dihedral angle fine while a corner is nearly flat, so
the corpus meshes had scaled Jacobians down to 0.01-0.07. The objective
is now the smaller of the dihedral sine and the scaled Jacobian at the
worst corner (the measure analysts check, Knupp 2001), weighted so a
Jacobian of 0.3 (the skill's limit) counts as a 30 degree dihedral
angle (the schedule's target): the Jacobian decides only near that
limit. The existing edge removal, multi-face removal, smoothing and
insertion then remove the needles.

Skill tet10 min SJ: sphere-on-plate 0.092 -> 0.335, filleted-bracket
0.021 -> 0.318 (both pass, nothing marked). Default-size tet10:
thin-ribs 0.240, shallow-groove 0.321, rounded-box 0.311.

The strong-relaxation test relaxes below 0.45: nothing is left below
0.3. Literature note in docs/meshing/literature.md.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo

docs/meshing/literature.md

@@ -402,7 +402,10 @@ Delaunay methods with Voronoi/ODT improvement, then (2) all-hex and hex-dominant
   (barycentres of boundary faces, of the tetrahedron, midpoints of boundary edges, and a point inside off a flat
   boundary edge). Deviations: the inserted vertex takes the Delaunay cavity rather than the optimal cut of §3.4; each pass
   smooths and flips the tetrahedra below sin 40° and inserts only when the worst did not improve; passes and the
-  insertion list are capped. Objective: the minimum dihedral sine. Every operation is a checked replacement of a region
+  insertion list are capped. Objective: the smaller of the minimum dihedral sine and the scaled Jacobian at the worst
+  corner weighted so that a Jacobian of 0.3 counts as a 30° dihedral angle: the sine misses needles (every dihedral
+  angle fine, one corner nearly flat; Shewchuk 2002); the scaled Jacobian analysts check (Knupp 2001, B6.6) catches
+  them, and with the weight it decides only near that limit. Every operation is a checked replacement of a region
   (positive by exact `orient3d`, faces matched with opposite orientation, removed vertices fully inside), so the mesh is
   valid after each step.