feat(python): classify buildings + emit chunk_CC_RR_buildings.json sidecar

[nigel-hall-codes]

Per building, emit classification facts (not template choices) into a new per-chunk sidecar, mirroring the existing _names/_parked sidecar pattern.

Includes: neighborhood (point-in-polygon), footprint_shape, width/depth, floor_count, ranked street_facades[] (corner-building correct, design D2), and footprint_hash per the normative algorithm (data-model.md §6.1). Adds --neighborhoods and the --templates gate to sfmap_bake.py.

Seams: osm.py (BuildingWay), chunk.py (classify), serialize.py (sidecar).

Acceptance: baking with --templates writes chunk_CC_RR_buildings.json matching data-model.md §1; deterministic across re-bakes.

From design #266 (sysdesign).