feat: add mesh-hygiene-audit example

[TMHSDigital]

Summary

• New mesh-hygiene-audit gallery example: stepped street electrical pedestal with engine-ingest topology gates (no ngons/loose verts, manifold edges, no zero-area faces, positive signed volume, Euler V-E+F==2).
• Dual-panel DIRTY vs CLEAN still; contact sheet beside pinned set; gallery/manifest/smoke/README/ROADMAP wired (34→35 examples, Game pipeline 7→8).
• Falsified each defect class on Blender 5.1.2 and 4.5.11 LTS; measured clean topology 24/44/22, volume 0.989248.

Contract (live-proven)

Gate	Measured (5.1.2 = 4.5.11)
verts/edges/faces / Euler	24 / 44 / 22 / 2
volume / min_area	0.989248 / 4.850e-02
ngons, loose, nonman, boundary, zero_area	all 0

Falsification (live)

Probe	Exit	Notes
loose vert	4	degree-0 vert
delete side face	5	boundary_edges=4
dissolve edge → ngon	3	1 ngon
flip all faces	7	volume −0.989248
collapse face → zero area	6	min_area=0

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

Visual passes

1. 1280×720 PNG vs Layer 1 (Standard transform, dark studio).
2. Named failure: v1 loose bead teleported toward CLEAN (local 3.5); fixed to front of dirty. Broken dual-panel is the still itself.
3. Preview webp 1200×675 at card size.
4. build_gallery.py + Playwright: desktop 1280×4000 full gallery, mobile ~390, detail page (lazy-load ok).
5. Contact sheet: docs/gallery/contact-sheets/mesh-hygiene-audit-contact-sheet.webp — mean luma armature-bend 0.279, damped-track 0.172, bmesh-gear 0.305, hygiene 0.357 (elevated by intentional dirty emission; stage still dark, wedge present, dual-panel thumbnail-legible).

Iterations: 4 (bead placement, saturation/emission, camera fill + labels, final frame).

Evidence labels

• Live run: checks + falsification both binaries; EEVEE still; gallery HTML numbers; Playwright screenshots.
• Inspection only: Cross-ref phrasing; 4.5/5.1 API name parity (byte-identical topology math).

Test plan

• blender-smoke 4.5 LTS + 5.1 green on PR head
• validate-counts / validate-manifest / drift-check
• Socket Security clear