Transit stops near a point

A filtered view over Overture's base/infrastructure `subtype='transit'`
rows (the same theme infrastructure_at reads), restricted to real,
boardable stop classes: bus_stop, bus_station, railway_station,
railway_halt, subway_station, tram_stop, ferry_terminal,
aerialway_station. Unfiltered, that layer is dominated by
bicycle_parking and by platform/stop_position — OSM's per-geometry
re-tagging of the same physical stop — which this tool never returns
by default; if zero stop-class rows are within radius_m it falls back
to platform/stop_position rows instead of an empty answer, and says so
in "note". `kind` restricts the search to exactly one class (any of
the stop classes above, or "platform"/"stop_position" directly);
an unrecognized kind returns a bad_request naming the accepted values.

Returns {"center", "radius_m", "results": [{"id", "kind", "name",
"distance_m"}, ...], "total_in_range"}, plus "truncated": true and an
explanatory "note" whenever fewer rows came back than matched, and a
"note" when the fallback fired or the search found nothing at all. id
is the GERS id, usable with other GERS-keyed tools. No raw geometry and
no schedules or live arrivals — Overture base/infrastructure is a
static OpenStreetMap conflation, and neither exists in it even in
principle; a caller wanting "next bus" needs a live transit API.

An empty results list is a valid answer, not an error: base-theme
coverage is OSM-derived and patchy, and "no stop within radius_m" is a
real finding. radius_m echoes the effective radius, which may be lower
than requested (large values are clamped).

Returns a structured {"error": ...} if upstream is unavailable or the
dataset is missing geometry/bbox, and {"error": "bad_request"} for a
non-finite or out-of-range coordinate, or an unrecognized kind.