feat: add prop-origin-transform example

[TMHSDigital]

Summary

• New prop-origin-transform gallery example: street pedestal + bolted accessory proving scale apply (1,1,1), local min.z==0, world AABB delta 0, bare-parent trap (~0.43 m jump), MPI restore (~3e-8), and stale matrix_world until view_layer.update().
• Dual-panel TRAP vs MPI KEEP still; contact sheet; gallery/manifest/smoke/README/ROADMAP (35→36 examples, Game pipeline 8→9).
• Extends parent-inverse-orrery without retreading orbits.

Contract (live-proven, byte-identical 5.1.2 / 4.5.11)

Gate	Measured
scale after bake	(1,1,1)
local min.z / XY center	0 / centered
world AABB delta	0
bare parent jump	0.428275
MPI restore err	2.980e-08
stale matrix before update	0

Falsification (live)

Probe	Result
skip scale apply	scale stays (1.15, 0.92, 1.08)
skip origin bake	min.z=-0.756
skip MPI	accessory remains jumped 0.428

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

Visual passes

1–5: Layer 1 studio; trap made readable via ghost expected-seat + jumped accessory (4 iterations: crop/float/ghost); preview webp; build_gallery.py + Playwright desktop/mobile/detail; contact sheet docs/gallery/contact-sheets/prop-origin-transform-contact-sheet.webp (luma 0.225 vs cal 0.17–0.30).

Evidence

• Live: checks + falsify both binaries; EEVEE still; HTML audit; Playwright.
• Inspection: cross-ref phrasing only.

Test plan

• blender-smoke 4.5 + 5.1
• validate-counts / manifest / drift
• Socket clear