feat: add gp-lineart-contour example

[TMHSDigital]

Summary

• New gallery example gp-lineart-contour: GPv3 + modifiers.new(..., \"LINEART\") with source_type='OBJECT', depsgraph-evaluated silhouette strokes on a faceted crystal.
• Version trap: thickness on 4.5, AttributeError on 5.1 — portable path is radius.
• Counts 33→34; gallery.json, plugin manifest, blender-smoke, README, ROADMAP; contact sheet committed.

Contract witnessed (live run)

Binary	Path	Reported	Contour
5.1.2	.scratch/blender-5.1.2-windows-x64/blender.exe	(5, 1, 2) / 5.1.2	10 strokes / 34 points; thickness=AttributeError
4.5.11 LTS	.scratch/blender-4.5.11-windows-x64/blender.exe	(4, 5, 11) / 4.5.11 LTS	10 strokes / 34 points; thickness=45

Also proven in-check: clear source_object → 0; contour+crease off → 0; restore recovers 10/34.

Falsification (live run on 5.1.2)

• Force source_object = None at build → exit 4 (round-trip)
• Raise POINT_MIN to 999 → exit 5 (points=34 < 999)
• Restored after each probe

Visual passes

• Iterations: 2 (draft neon outline → thicker radius 0.028 + slight emission on crystal)
• Pass 1: Standard, designed crystal, cyan contours, dark studio, no helpers
• Pass 2: without LINEART the cyan silhouette vanishes — that is the visual difference
• Pass 3: preview webp reads as neon-outlined crystal at card size
• Pass 4: Playwright detail page confirms thickness/10 claims; gallery regenerated to 34 cards
• Pass 5: contact sheet — meanY vs cal: armature-bend 0.277, damped-track 0.174, bmesh-gear 0.305, candidate 0.211. Default stage (no deviation). Neon outline is the contract; sits with the dark-studio lineup.

Evidence labeling

• Live run: both Blender checks, falsification, still render, contact-sheet luminance, Playwright detail
• Inspection only: generated HTML claim scan after build_gallery.py

Test plan

• blender-smoke 4.5 + 5.1 green on PR head
• validate + drift-check green
• Socket Security resolved
• Local 5.1.2 + 4.5.11 check-only commands for examples/gp-lineart-contour/gp_lineart_contour.py