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.

Tools/README.md

@@ -13,6 +13,8 @@ Repeatable import/export and processing helpers. Anything that was done twice by
 ## Helpers
 
 - `check-lfs.sh` — repository guard: fails if `git-lfs` or the `lfs` filter is missing, or if an LFS-tracked file was committed as a plain blob.
+- `street_mesh.py` — road, kerbs, and sidewalks on the DEM, in the project frame; kerbs flush at the three crossings.
+- `terrain_from_dem.py` — terrain grid from the committed DEM, with building footprints cut out.
 - `blosm_blockout.py` — headless Blosm import of the committed `.osm` extract into a `.blend`, with a per-building scale report. Exact invocation in `Art/blender/README.md`.
 - `commons_fetch.py` — Wikimedia Commons reference fetcher. Search or exact `File:` titles, 1600 px thumbnails, provenance `sidecar.json` per folder. Writes only into the gitignored `Art/reference/`; reference images are never committed.