Copenhagen Phase 1: scaffolding + area + OSM download

- pyproject.toml with all deps (geopandas, contextily, partridge, etc.)
- config/: area.json (3 OSM boundary relations), modes.yaml (subway/s_tog/
  light_rail/regional/bus, S-tog scoped to route=light_rail network=Takst),
  styling.yaml (zorder/widths/colours/palette/mask/labels)
- build_area.py: fetch 3 relations via OSM API, stitch rings, dissolve to
  area.gpkg/area.geojson (City Pass approximation)
- download_osm.py: per-mode Overpass (mirror+backoff, out geom + recurse for
  stops), writes {mode}.gpkg (lines+stops) + query text
- download_gtfs.py / gtfs_to_geopackage.py: stubs (blocked on Rejseplanen)
- data/ gitignored (regenerable); output/ tracked

copenhagen/scripts/gtfs_to_geopackage.py

@@ -0,0 +1,42 @@
+#!/usr/bin/env python3
+"""Convert raw GTFS txt files into portable GeoPackage layers + a colour table.
+
+STATUS: BLOCKED on download_gtfs.py (no feed URL yet).
+
+Intended outputs (data/processed):
+    gtfs_shapes.gpkg   (shapes.txt -> LineString per shape_id, EPSG:4326)
+    gtfs_stops.gpkg    (stops.txt -> Point per stop, EPSG:4326)
+    route_colors.csv   (route_id, route_short_name, route_type, route_color)
+
+Uses partridge for fast GTFS parsing. prepare.py reads these when present and
+falls back to OSM-only data when absent.
+"""
+import sys
+from pathlib import Path
+
+from _common import GTFS_RAW, PROCESSED
+
+
+def main():
+    if not (GTFS_RAW / "routes.txt").exists():
+        print(
+            "gtfs_to_geopackage: BLOCKED — no GTFS data found in "
+            f"{GTFS_RAW}. Run download_gtfs.py first once a feed URL is set.",
+            file=sys.stderr,
+        )
+        sys.exit(2)
+
+    # TODO (when GTFS available):
+    #   import partridge as pt
+    #   import geopandas as gpd
+    #   from shapely.geometry import LineString, Point
+    #   feed = pt.load_geo_feed(str(GTFS_RAW))
+    #   shapes -> gtfs_shapes.gpkg (LineString per shape_id)
+    #   stops  -> gtfs_stops.gpkg
+    #   routes -> route_colors.csv (route_id, route_short_name, route_type, route_color)
+    print("gtfs_to_geopackage: not yet implemented (GTFS feed unavailable).")
+    sys.exit(2)
+
+
+if __name__ == "__main__":
+    main()