Add bus stop markers from stops layer

- plot_bus_stops(): loads bus stops from master.gpkg stops layer (1610
  points), draws small white-filled circles (1.5pt) at each location
- stops layer loaded in main() alongside stations
- 'bus' added to stations.styles and marker.size in styling.yaml
- bus stops respect --no-stops and --no-buses / --modes filters
- bus marker zorder sits just above bus lines

copenhagen/config/styling.yaml

@@ -72,7 +72,7 @@ basemap:
 
 stations:
   show: true              # draw station markers (symbols without text)
-  styles: [metro, s_tog, regional]
+  styles: [metro, s_tog, regional, bus]
   marker:
     shape: circle         # circle | square
     fill: white
@@ -81,6 +81,7 @@ stations:
       metro: 3.5
       s_tog: 3.0
       regional: 2.5
+      bus: 1.5
     linewidth: 0.8
 
 labels: