feat: add tavern-stool and iron-cauldron showcase pieces

[TMHSDigital]

Summary

Prompt list was already shipped. Next two ROADMAP props:

• tavern-stool — round seat, turned splayed legs, stretchers, iron ferrules.
• iron-cauldron — bulged open iron pot hanging from a timber tripod with bail and hook.

Showcase count 22 → 24. Did not touch examples, skills, snippets, rules, templates, gallery_framing.py, LICENSE, VERSION, CHANGELOG, or smoke/pages/release workflows.

Next backlog (restocked): wooden ladder, hay bale.

tavern-stool — live run (.scratch binaries)

Axis	Declared	4.5.11 / 5.1.2 / 5.2.1
Base tris	5250–5550	5396 / 5396 / 5396
LOD1 / LOD2	0.32–0.62 / 0.10–0.35	0.5000 / 0.2198 all three
Materials	2, ≥24 wood, ≥16 metal	2542 wood, 40 metal
AABB	(0.309, 0.309, 0.467) ± 0.01	(0.3093, 0.3093, 0.4670), zmin 0.002
Collider	≤ 140	96
Export	size > 0	380604 / 380604 / 380588 B

Exits: default 0 / --skip-decimate 9 (LOD1 ratio) / --nope 2 on all three. Dual 5.2.1 defaults matched. Smoke wall-clock ~3.3s / 1.9s / 2.2s (4.5 / 5.1 / 5.2).

Composes mesh-editing-and-bmesh, bake-high-to-low, depsgraph-and-evaluated-data, engine-export-presets + copied snippets bake_normal_high_to_low, setup_bake_target_image, lod_chain / decimate_to_budget, convex_hull_collider, export_preset_unity.

iron-cauldron — live run (.scratch binaries)

Axis	Declared	4.5.11 / 5.1.2 / 5.2.1
Base tris	6850–7200	7012 / 7012 / 7012
LOD1 / LOD2	0.32–0.62 / 0.10–0.35	0.5000 / 0.2199 all three
Materials	2, ≥12 wood, ≥24 metal	2754 wood, 706 metal
AABB	(0.572, 0.558, 0.786) ± 0.01	(0.5723, 0.5582, 0.7855), zmin 0.002
Collider	≤ 180	130
Export	size > 0	501796 / 501796 / 501780 B

Exits: default 0 / --skip-decimate 9 (LOD1 ratio) / --nope 2 on all three. Dual 5.2.1 defaults matched. Smoke wall-clock ~5.3s / 2.8s / 3.1s.

Composes the same pipeline.

Test plan

• Local 4.5.11 / 5.1.2 / 5.2.1 matrix for both pieces
• Gallery regen
• CI Validate + blender-smoke 4.5 / 5.2 / labeled 5.1 + Socket

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