feat: add campfire and market-stall showcase pieces

[TMHSDigital]

Summary

• Fourth showcase piece campfire: cobble ring, ash mound, crossed logs, through UVs / bake / LOD / collider / Unity glTF.
• Fifth showcase piece market-stall: timber frame, striped awning, counter, same pipeline.
• Falsifier --skip-decimate exits 9 on the LOD1 ratio budget for both, on 4.5.11 / 5.1.2 / 5.2.1.
• No existing examples, skills, snippets, rules, templates, gallery_framing.py, LICENSE, VERSION, CHANGELOG.md, or smoke/pages/release workflows were touched.

Test plan

• Default and --skip-decimate on 4.5.11, 5.1.2, 5.2.1 (headless)
• Two consecutive 5.2.1 defaults identical (determinism)
• argparse unknown flag exits 2
• 5.2.1 --output stills; check_framing with no deviation=
• CI: Validate, drift-check, Socket, Blender 4.5 / 5.1 / 5.2 smoke (5.1 via REST needs-5.1)

campfire

Binaries (live): .scratch/blender-4.5.11-windows-x64/blender.exe reports 4.5.11 LTS; .scratch/blender-5.1.2-windows-x64/blender.exe reports 5.1.2; .scratch/blender-5.2.1-windows-x64/blender.exe reports 5.2.1 LTS.

Axis	Declared	4.5.11 / 5.1.2 / 5.2.1
Base tris	7400–7650	7528 / 7528 / 7528
LOD1	0.32–0.62	0.5000 / 0.5000 / 0.5000
LOD2	0.10–0.35	0.2200 / 0.2200 / 0.2200
Mats	3 distinct, ≥24 wood, ≥8 ash	3 / 116 wood / 18 ash
UVs	0..1, overlap ≤ 1e-5	in range, 0
AABB m	(0.964, 0.950, 0.252) ± 0.01	(0.9641, 0.9495, 0.2521), zmin 0
Collider	≤ 160	105
Export	> 0	548944 / 548944 / 548936

	4.5.11	5.1.2	5.2.1
Default exit	0	0	0
--skip-decimate	9	9	9
argparse --nope			2

Falsifier violates LOD1 ratio (1.0 vs band 0.32–0.62). Two consecutive 5.2.1 defaults: identical 7528 / r1=0.5000 / bbox.

Added smoke wall-clock (check-only): 6.67s / 3.51s / 3.71s.

Framing (5.2.1, live): fill x=0.784 y=0.639 (max 0.784 in band); margins ≥ 0.100. No deviation=.

Composes: skills mesh-editing-and-bmesh, bake-high-to-low, depsgraph-and-evaluated-data, engine-export-presets; snippets bake_normal_high_to_low.py, setup_bake_target_image.py, lod_chain.py / decimate_to_budget.py, convex_hull_collider.py, export_preset_unity.py (copied).

market-stall

Axis	Declared	4.5.11 / 5.1.2 / 5.2.1
Base tris	2140–2350	2244 / 2244 / 2244
LOD1	0.32–0.62	0.5000 / 0.5000 / 0.5000
LOD2	0.10–0.35	0.2193 / 0.2193 / 0.2193
Mats	3 distinct, ≥16 faces/stripe	3 / 48 / 48
UVs	0..1, overlap ≤ 1e-5	in range, 0
AABB m	(1.360, 0.964, 1.743) ± 0.01	(1.3600, 0.9639, 1.7430), zmin 0
Collider	≤ 80	28
Export	> 0	163992 / 163992 / 163968

	4.5.11	5.1.2	5.2.1
Default exit	0	0	0
--skip-decimate	9	9	9
argparse --nope			2

Falsifier violates LOD1 ratio (1.0 vs band 0.32–0.62). Two consecutive 5.2.1 defaults identical.

Added smoke wall-clock (check-only): 1.42s / 1.21s / 1.31s.

Framing (5.2.1, live): fill x=0.338 y=0.839 (max 0.839 in band); margins ≥ 0.039. No deviation=.

Composes: same skills/snippets as campfire.

Evidence label

Live headless runs: all budget numbers, exit codes, wall-clock, framing prints, argparse 2. Inspection only: gallery HTML alts / data-tags after scripts/build_gallery.py.

DECIMATE COLLAPSE matched across series here; gate remains a ratio band. glTF bytes differ by a few bytes. Bake pixels stochastic (has_data + FINISHED).