feat(windkarte): slugPrefix enforcement, name→gebiets_nr, name field removed

- RustyCMS: SchemaDefinition.slug_prefix + auto-prepend in create_entry
- wind_area/wind_map schemas: slugPrefix config, name field removed
- wind_area entries: name→gebiets_nr (faktische Gebietsnummer, GeoJSON-Join-Key)
- WindkarteMap/WindAreaPanel: Join + Anzeige auf gebiets_nr

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/lib/components/WindkarteMap.svelte

@@ -73,7 +73,7 @@
       maxZoom: 16,
     }).addTo(map);
 
-    const byName = Object.fromEntries(areas.map((a) => [a.name, a]));
+    const byNr = Object.fromEntries(areas.map((a) => [a.gebiets_nr, a]));
 
     try {
       const geoRes = await fetch(geojsonUrl);
@@ -85,7 +85,7 @@
           return style(s, false);
         },
         onEachFeature: (feature, layer) => {
-          const cmsArea = byName[feature.properties?.name] ?? null;
+          const cmsArea = byNr[feature.properties?.name] ?? null;
           if (cmsArea) feature.properties.cms = cmsArea;
 
           layer.on("click", async () => {