feat(geo): cross-check block heights against Mapbox building data

New Geo/tools/mapbox_buildings.py (stdlib urllib) Tilequeries
mapbox-streets-v8 / layer building at each building centroid and merges
height/min_height/type with our OSM height + source (tag > levels > guess,
reusing block_height_report.classify_height). Reports matches, close calls,
disagreements (sorted worst first), our-only and mapbox-only cases, and writes
optional JSON.

First run over 72 buildings: 58 match, 5 close, 3 disagree, 6 non-building.
- Mapbox independently classifies our roof/canopy/shelter volumes as roof,
  canopy or shelter -> corroborates the 0.1.2 finding.
- The 3 disagreements are rear building=yes/apartments structures rendering at
  our 2-level guess (6.4 m) vs Mapbox's 3.0 m.
- Every levels x 3.2 m building is ~0.6 m per 6 levels taller than Mapbox
  implies, i.e. Mapbox suggests 3.1 m per level. Recorded, not applied.

classify_height() now also treats building=canopy as a non-building volume
(found by this cross-check), with tests.

Data handling: Mapbox terms restrict persisting/redistributing their data, so
.gitignore covers Geo/raw/mapbox-cache/ and Geo/verification/*mapbox*; the tool
refuses to cache a response containing the token, and the token is never written
to the cache, report or JSON. Token comes from the ignored .env.

Also: 17 new tests (29 total) for the compare/nearest/centroid/render helpers
and the canopy rule; Geo/README inventory row; architecture 05 + architecture.md
tools table updated per the new upkeep rule.

Geo/README.md

@@ -27,6 +27,7 @@ Tools that build 3D content from these sources live next to their output in `Art
 | `elevation_probe.py` | Samples 3DEP for relief and records the baseline for the release checks |
 | `dem_stats.py` | Stdlib reader for the tiled GeoTIFF the 3DEP service returns; GDAL does not run on this host |
 | `asset_metadata.py` | Writes and audits `<asset>.geo.json` sidecars: position, provenance, conversion |
+| `mapbox_buildings.py` | Cross-checks every building's height against Mapbox `mapbox-streets-v8` building data (Tilequery per centroid), merging our OSM height + source with theirs and flagging matches, close, disagreements, non-building volumes. Needs `MAPBOX_ACCESS_TOKEN` in `.env`; caches responses under `Geo/raw/mapbox-cache/`, and **both the cache and its report are gitignored** (Mapbox terms restrict redistribution) |
 
 ## Unit boundary