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.

Art/blender/README.md

@@ -61,6 +61,27 @@ Spot checks against the measured cross-sections:
 
 That reproduces both the 3.4 m eastward fall and the ~2 % crown, so the DEM, the cross-sections, and this mesh agree.
 
+## Street corridor
+
+`street/street-2026-11-06.blend` — road, kerbs, and both sidewalks, built by `Tools/street_mesh.py` from the DEM and the centreline.
+
+```bash
+B=/var/lib/flatpak/app/org.blender.Blender/x86_64/stable/active/files
+LD_LIBRARY_PATH="$B/blender/lib" "$B/blender/blender" -b --factory-startup \
+  --python Tools/street_mesh.py -- \
+  --osm Geo/raw/osm-api-map-2026-11-06.osm \
+  --dem Geo/raw/dem-3dep-1m-26911-2026-11-06.tif \
+  --out Art/blender/street/street-2026-11-06.blend
+```
+
+- `Road_Hollywood`: 8 120 verts, 7 812 faces, carriageway −10.5…+10.5 m, DEM elevations plus a 2 cm lift so it does not z-fight the terrain.
+- `Sidewalk_South` 4.0 m wide, `Sidewalk_North` 5.3 m wide, both raised by the kerb height.
+- `Kerb_South`, `Kerb_North`: vertical faces, mostly **0.13 m** — the 0.15 m assumption minus nothing on the road side — and flushed to 0 within ±2.5 m of each signalised crossing with a 1.5 m blend. Measured from the built mesh: 256 steps at 0.13 m, 15 flush, a few in transition.
+
+Crown check on the built mesh at mid-block: gutter −10.5 m → +0.99, −5 m → +1.38, centre → +1.52, +5 m → +1.58, +10.5 m → +1.52. The crown sits just north of the centreline, as the cross-sections said.
+
+Assumptions, recorded rather than hidden: kerb upstand 0.15 m (DEM cannot resolve it), sidewalk widths from the setback arithmetic, and crossing ramps modelled as kerb flushes rather than graded ramps. Crossing markings, kerb radii at the junctions, driveway aprons, drainage inlets, and pavement joints are **not** modelled.
+
 ## Scale check (blockout, 2026-11-06)
 
 Blender works in metres, and the imported meshes match the OSM geometry, so the blockout is 1:1 before any Unreal export: