mesh: the tet report carries the scaled Jacobian; both metrics tested on the same tets (#547)

The dihedral range and mesh.quality's scaled Jacobian were both right:
they are computed by the same function on the same final corners (tet4
and tet10 give identical numbers), but a dihedral range does not bound
the corner scaled Jacobian. A needle has dihedral angles near 60 and 90
degrees and a nearly flat apex corner. Before 417c0c88 sphere-on-plate
at size 4 had dihedrals 36.3-141.6 and 106 needles below SJ 0.2 (min
0.095); now 36.0-137.6 and min SJ 0.351.

The mesher's report now carries min_scaled_jacobian so it cannot read
as all-good while needles remain.

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo

crates/engine/src/cmd/mesh.rs

@@ -250,6 +250,7 @@ pub(super) fn quality_json(q: &TetQuality) -> Value {
         "max_dihedral": q.max_dihedral,
         "min_radius_ratio": q.min_radius_ratio,
         "mean_radius_ratio": q.mean_radius_ratio,
+        "min_scaled_jacobian": q.min_scaled_jacobian,
         "slivers": q.slivers,
         "inadmissible": q.inadmissible,
     })