Some bus stop platform nodes in OSM are not members of any route
relation (e.g. Borgergade). These were missed by the route-membership
download approach. Now download_osm.py:
- tracks bus platform node ids captured by route queries
- runs a supplementary query for all highway=bus_stop + platform nodes
- appends orphans (with empty route_refs) to the bus stops layer
render.py: orphan stops (empty route_refs) fall back to distance
clustering instead of route-membership grouping.
Results: 1164 route-member stops + 707 orphans = 1871 total
-> 1370 after clip -> 1049 markers after grouping