Use platform nodes + route membership for bus stop clustering

Replaces distance-based clustering with route-membership grouping:
- download_osm.py: collect route_refs per stop node; use platform roles
  for bus stops, stop roles for rail stops
- prepare.py: carry route_refs through to master.gpkg
- render.py: group_by_route_membership() uses union-find to cluster
  same-name stops sharing at least one route into one marker; stops on
  disjoint routes are kept separate. No distance threshold needed.

Results: 786 bus platforms -> 465 markers (was 1610 -> 781).
Veksøvej: 2 platforms sharing routes 2A+5C -> 1 marker.
Peter Bangs Vej: 7 platforms on routes 10/21/22/4A/7A -> 2 markers.

copenhagen/scripts/download_osm.py

@@ -8,7 +8,8 @@ fallback + exponential backoff) and writes:
 
 Lines: one MultiLineString per route relation (concatenation of member way
 geometries), carrying ref/name/network/colour/operator/route/mode tags.
-Stops: one Point per stop/platform node member, carrying ref/name/mode.
+Stops: one Point per platform node member, carrying ref/name/mode/route_refs
+(route refs of routes using this stop, for disambiguation).
 """
 import sys
 import time
@@ -28,7 +29,11 @@ MIRRORS = [
 ]
 
 PLATFORM_ROLES = {"platform", "platform_entry", "platform_exit"}
-STOP_ROLES = {"stop", "stop_entry", "stop_exit", "platform", "platform_entry", "platform_exit"}
+STOP_ROLES = {"stop", "stop_entry", "stop_exit", "stop_entry_only", "stop_exit_only"}
+# bus stops: use platform nodes (where passengers wait)
+# rail stops: use stop nodes (platforms are often areas, stop nodes are reliable points)
+BUS_STOP_ROLES = PLATFORM_ROLES
+RAIL_STOP_ROLES = STOP_ROLES | PLATFORM_ROLES
 
 
 def build_query(mode_cfg, bbox):
@@ -72,19 +77,25 @@ def overpass(ql):
 
 
 def parse(data, mode):
+    is_bus = mode == "bus"
+    stop_roles = BUS_STOP_ROLES if is_bus else RAIL_STOP_ROLES
+
     nodes = {}
     for e in data["elements"]:
         if e["type"] == "node":
             nodes[e["id"]] = e
 
-    lines, stops = [], []
-    stop_seen = set()
+    lines = []
+    # collect route_refs per stop node: {node_id: set(route_refs)}
+    node_routes = {}
     for e in data["elements"]:
         if e["type"] != "relation" or "tags" not in e:
             continue
         tags = e["tags"]
         if tags.get("route") is None:
             continue
+        route_ref = tags.get("ref")
+        # collect line geometries
         segs = []
         for m in e["members"]:
             if m["type"] == "way" and "geometry" in m and m.get("role") not in PLATFORM_ROLES:
@@ -96,7 +107,7 @@ def parse(data, mode):
             continue
         lines.append({
             "mode": mode,
-            "ref": tags.get("ref"),
+            "ref": route_ref,
             "name": tags.get("name"),
             "network": tags.get("network"),
             "colour": tags.get("colour"),
@@ -104,25 +115,37 @@ def parse(data, mode):
             "route": tags.get("route"),
             "geometry": geom,
         })
+        # record route_ref on each stop member node
         for m in e["members"]:
-            if m["type"] != "node" or m.get("role") not in STOP_ROLES:
+            if m["type"] != "node" or m.get("role") not in stop_roles:
                 continue
             nid = m["ref"]
-            if nid not in nodes or nid in stop_seen:
+            if nid not in nodes:
                 continue
-            nd = nodes[nid]
-            if "lat" not in nd or "lon" not in nd:
-                continue
-            stop_seen.add(nid)
-            ntags = nd.get("tags", {})
-            stops.append({
-                "mode": mode,
-                "name": ntags.get("name") or ntags.get("public_transport") or "stop",
-                "ref": ntags.get("ref"),
-                "public_transport": ntags.get("public_transport"),
-                "railway": ntags.get("railway"),
-                "geometry": Point(nd["lon"], nd["lat"]),
-            })
+            node_routes.setdefault(nid, set())
+            if route_ref:
+                node_routes[nid].add(route_ref)
+
+    # build stops from collected nodes
+    stops = []
+    stop_seen = set()
+    for nid, routes in node_routes.items():
+        if nid in stop_seen:
+            continue
+        nd = nodes[nid]
+        if "lat" not in nd or "lon" not in nd:
+            continue
+        stop_seen.add(nid)
+        ntags = nd.get("tags", {})
+        stops.append({
+            "mode": mode,
+            "name": ntags.get("name") or ntags.get("public_transport") or "stop",
+            "ref": ntags.get("ref"),
+            "public_transport": ntags.get("public_transport"),
+            "railway": ntags.get("railway"),
+            "route_refs": ";".join(sorted(routes)),
+            "geometry": Point(nd["lon"], nd["lat"]),
+        })
     return lines, stops