Make station labels opt-in; add station markers (symbols without text)

- labels: off by default (was on). Enable via --labels flag or
  styling.yaml labels.show: true. Previously --no-labels opted out.
- stations: new markers layer -- small white-filled circles with dark
  border at each station, sized by mode (metro 3.5pt, s_tog 3.0pt,
  regional 2.5pt). On by default; disable via --no-stops.
- markers respect --modes filter (only mark stations for drawn layers)
- styling.yaml: add stations section (shape/fill/edge/size/linewidth)
- classify_station() helper deduplicates the metro/s_tog/regional logic
- fix attribution to Esri (was CARTO)

copenhagen/config/styling.yaml

@@ -70,8 +70,21 @@ basemap:
   provider: Esri.WorldGrayCanvas
   zoom: 14
 
+stations:
+  show: true              # draw station markers (symbols without text)
+  styles: [metro, s_tog, regional]
+  marker:
+    shape: circle         # circle | square
+    fill: white
+    edge: "#2b2b2b"
+    size:                 # diameter in points
+      metro: 3.5
+      s_tog: 3.0
+      regional: 2.5
+    linewidth: 0.8
+
 labels:
-  show: true
+  show: false             # off by default; enable via --labels
   styles: [metro, s_tog]   # which station types to label
   min_fontsize: 5
   max_fontsize: 9