fix: rebuild watchtower as a timber lookout with a shake roof

[TMHSDigital]

Summary

• Rebuild watchtower. The v0.70 still was a 4-sided cone jammed inside a railing box — unreadable as a lookout.
• Now: posts through a plank deck with a ladder hatch, lower-bay X-braces, kick plates, iron shoes/straps, and a well-style coursed shake roof with eaves. Third material slot for the shakes.
• Budgets refit to the new mesh. --skip-decimate still exits 9 on LOD1.

Test plan

Local binaries: 4.5.11 LTS, 5.1.2, 5.2.1 LTS. Two consecutive 5.2.1 defaults matched. argparse --nope exits 2 on all three. --skip-decimate exits 9 on LOD1 on all three. check_framing with no deviation=. Hero Cycles 5.2.1.

Axis	Declared	4.5.11 / 5.1.2 / 5.2.1
Base tris	5110–5330	5220 / 5220 / 5220
LOD1	0.32–0.62	0.5000 / 0.5000 / 0.5000
LOD2	0.10–0.35	0.2199 / 0.2199 / 0.2199
Materials	3 distinct, ≥24 metal, ≥40 roof	84 metal, 126 roof
UVs	0..1, overlap ≤ 1e-5	in range, 0
AABB	(1.434, 1.434, 1.982) ± 0.01	(1.4340, 1.4340, 1.9818), zmin 0
Collider	≤ 80	56
Export	> 0	374376 / 374376 / 374360

Default 0 / falsifier 9 / argparse 2 on all three. Falsifier violates LOD1 ratio. Smoke wall-clock (check-only): 3428 / 2295 / 2378 ms.

Live run: default, skip, argparse, two 5.2 defaults, Cycles still, gallery alts.
Inspection only: CI 4.5 float vs local 4.5.11; Socket.