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.

Geo/verification/2026-11-06-cross-sections.md

@@ -44,6 +44,10 @@ Consequence: kerb height and shape are an **assumption** until measured or obser
 
 `Art/blender/terrain/terrain-2026-11-06.blend` samples the DEM on a 2 m grid and reproduces these numbers: origin Z 0.00, Orange Drive end +3.39, south gutter +0.93, road centre +1.38, north sidewalk +1.43 relative to the origin ground. The crown therefore survives from DEM to mesh. See `Art/blender/README.md`.
 
+## Reproduced in the street mesh
+
+`Art/blender/street/street-2026-11-06.blend` carries the same numbers through to geometry: rule at mid-block reads +0.99 at the south gutter, +1.38 at −5 m, +1.52 at the centre, +1.58 at +5 m, +1.52 at the north gutter. Kerb faces measure 0.13 m and flush to zero at the crossings.
+
 ## Open
 
 - Kerb height, kerb radius, and ramp slope: assumption until surveyed or measured from photographs.