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/_common.py

@@ -0,0 +1,14 @@
+"""Shared paths and constants for the Copenhagen map scripts."""
+from pathlib import Path
+
+HERE = Path(__file__).resolve().parent
+CPH = HERE.parent
+CONFIG = CPH / "config"
+DATA = CPH / "data"
+RAW = DATA / "raw"
+OSM_RAW = RAW / "osm"
+GTFS_RAW = RAW / "gtfs"
+PROCESSED = DATA / "processed"
+OUTPUT = CPH / "output"
+
+UA = "jetlag-maps/0.1 (https://github.com/marvin/jetlag-maps)"