feat: road, kerbs, and sidewalks on the DEM

Tools/street_mesh.py builds the corridor in the project frame from the measured
profile: carriageway -10.5..+10.5 m, kerbs 0.15 m (0.13 m as built), sidewalks
4.0 m south and 5.3 m north, all elevations sampled from the DEM. Kerbs flush at
the three signalised crossings. Crown at mid-block reproduces the cross-sections
to the centimetre.

ROADMAP.md

@@ -42,7 +42,7 @@ Status detail in [Docs/setup.md](Docs/setup.md); workstation audit in [Docs/envi
 - [ ] Model hero façade for the El Capitan Entertainment Centre site.
 - [ ] Model surrounding block frontage.
 - [ ] Model simplified background buildings directly across Hollywood Boulevard.
-- [-] Build sidewalks, roads, and collision meshes. Terrain mesh from the DEM exists (`Art/blender/terrain/terrain-2026-11-06.blend`); sidewalks, roads, kerbs and collision are not built. Ground must follow the DEM: 3.94 m fall along the block, ~2 % crown between the gutters at ±10–11 m from the centreline, north sidewalk higher than south. Kerb height is an unresolved assumption — the DEM does not resolve it (`Geo/verification/2026-11-06-cross-sections.md`).
+- [-] Build sidewalks, roads, and collision meshes. Terrain, road, sidewalks and kerbs exist (`Art/blender/terrain/`, `street/`); collision and details (crossing markings, kerb radii, aprons) are not built. Ground must follow the DEM: 3.94 m fall along the block, ~2 % crown between the gutters at ±10–11 m from the centreline, north sidewalk higher than south. Kerb height is an unresolved assumption — the DEM does not resolve it (`Geo/verification/2026-11-06-cross-sections.md`).
 - [ ] Materials and look development for all exported assets.
 
 ### Gameplay