engine: bracket-hex sample, the partitioned bracket meshed all-hex and solved

file.sample bracket-hex: the corpus bracket split into 30 SolidCraft cells,
meshed by mesh.hex.blocks as one conforming hex20 mesh of 3 mm, clamped at
the upright and loaded at the foot. The sample's script finds the clamp and
load faces in every cell that has them. Its test matches the tip deflection
of a fine tet10 solution within 1 % and checks the clamp carries the load.

Closes #166

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

docs/examples.md

@@ -91,3 +91,23 @@ evenly by ΔT = 100 K, and clamps the foot's hole alone: the bracket then grows
 and a point moves α ΔT times its distance from the hole's axis. The upright's top moves −0.0432
 mm along x (within 2 %); the foot's end, 16 mm from the clamped bore, which cannot grow, moves
 0.0228 mm against 0.024 mm (within 6 %).
+
+## Hex-meshed bracket (`bracket-hex`)
+
+![Von Mises stress on the all-hex bracket, O-grids round both holes, peaking at the upright's hole](media/examples/bracket-hex.png)
+
+The same filleted bracket split into 30 cells in SolidCraft
+(`tests/corpus/filleted-bracket-blocks`: planar cuts through the legs and diagonal cuts round
+the holes and the fillet, each cell a six-sided block), meshed by `mesh.hex.blocks` as one
+conforming all-hex mesh: 5 778 hex20 elements of 3 mm, O-grids round the holes, graded through
+the fillet, every shared face meshed once. Steel; the upright's end clamped, 1 kN down on the
+foot's end. Linear static: about 2 s to open (the cells are rebuilt from the script) and 3 s to
+solve.
+
+**Look at:** the mesh (Prepare ▸ Mesh) — mapped blocks meeting face to face with no pyramids or
+tets — and the von Mises contours on the deformed shape: the stress runs round the fillet and
+peaks at 295 MPa at the upright's hole.
+
+**Check:** the tip of the foot moves 0.509 mm down, within 1 % of a 48 016-element tet10
+solution of the unpartitioned part (0.5093 mm, `crates/testkit/tests/bracket_blocks.rs`), and the
+clamp carries the whole 1 kN.