Add bus whitelist, route exclusions, crow-fly shape filter, and KML export

- modes.yaml: bus_whitelist (A-buses + selected refs) and exclude list
  (Snälltåget 083 night train — sparse crow-fly stubs)
- prepare.py: drop degenerate crow-fly shapes below 0.05 pts/km; apply
  bus whitelist and route exclusions from modes.yaml
- export_google_mymaps.py: new script — master.gpkg -> KML for Google
  My Maps import (stops, routes, boundary, coastline layers)
- coastline.kml: reference coastline layer for the KML export
- .gitignore: also ignore generated output/*.kml

copenhagen/config/modes.yaml

@@ -13,6 +13,23 @@
 # ORDER MATTERS: the styles listed here are also the priority order when a
 # pole is served by several modes (e.g. S-tog and regional trains share
 # platforms at hub stations — the higher style wins).
+# Hard exclusions: specific routes to drop entirely, keyed by (agency,
+# short name) — the pairing rule used everywhere else in this feed.
+# 083 (Snälltåget night train, Malmö-Stockholm): its in-area shapes are
+# sparse crow-fly stubs that draw as straight cuts across the map; the
+# long-distance train is not relevant for the city game, so skip it.
+# Bus whitelist: only these buses are included — there are far more city
+# bus routes than the game scale needs. Match on bus category (per
+# styling.yaml bus_filters) or on specific refs. Remove this section to
+# include all buses; with empty lists no buses are included.
+bus_whitelist:
+  categories: [A]   # all "A" city buses (1A, 2A, 4A, 6A, 9A, ...)
+  refs: ["21", "30", "31", "32", "33", "34", "35", "36", "37", "38", "39", "68", "77"]
+
+exclude:
+  - agency: Snälltåget AB
+    ref: "083"
+
 modes:
   metro:
     agencies: [Metroselskabet]