fix: seal water-trough hull; drop bellows

[TMHSDigital]

Summary

• water-trough: the old mesh was a slatted U (gap=0.16) shot end-on, so the basin had no sides and water sat in open air. Rebuilt as a continuous U-hull with plank end-caps and a water plane inside the rim.
• bellows: removed. The leather bag never read; ROADMAP marks it DROPPED rather than restocking.

Showcase count 21 → 20. Did not touch examples, skills, snippets, rules, templates, gallery_framing.py, LICENSE, VERSION, CHANGELOG, or smoke/pages/release workflows.

water-trough — live run (.scratch binaries)

Axis	Declared	4.5.11 / 5.1.2 / 5.2.1
Base tris	2320–2650	2484 / 2484 / 2484
LOD1 / LOD2	0.32–0.62 / 0.10–0.35	0.5000 and 0.2198 / 0.2198 / 0.2166
Materials	3, ≥24 metal, ≥6 water	192 metal, 6 water
AABB	(1.152, 0.568, 0.509) ± 0.01	(1.1520, 0.5680, 0.5086), zmin 0
Collider	≤ 80	32
Export	size > 0	180748 / 180748 / 180728 B

Exits: default 0 / --skip-decimate 9 (LOD1 ratio) / --nope 2 on all three. Dual 5.2.1 defaults matched.

Test plan

• Local 4.5.11 / 5.1.2 / 5.2.1 matrix for the trough
• Gallery regen; bellows card gone; trough alt/witnesses full sentence
• CI Validate + blender-smoke 4.5 / 5.2 / labeled 5.1 + Socket

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