ui(map): red overlay for excluded Bezirke, drop Leaflet attribution prefix

- Excluded-district shading switches from amber/yellow to a soft red
  (fill #fca5a5 at 0.3 opacity, stroke #c84545) — reads as "blocked"
  rather than "highlighted", which matches the meaning better.
- Drop the "Leaflet" attribution prefix (not legally required).
  Keep "© OpenStreetMap · © CARTO" — ODbL and CARTO's basemap terms
  both require attribution.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

web/static/map.js

@@ -155,9 +155,9 @@ function renderMarkers(payload) {
   ensureDistrictLayer(selectedDistricts);
 }
 
-// EXPERIMENT: faintly highlight Bezirke the user's filter EXCLUDES so the
-// active selection is obvious at a glance. When the filter is empty (no
-// district narrowing) the layer is hidden — nothing is excluded.
+// Faintly highlight Bezirke the user's filter EXCLUDES so the active
+// selection is obvious at a glance. When the filter is empty (no district
+// narrowing) the layer is hidden — nothing is excluded.
 function districtStyle(selectedSet) {
   const showShading = selectedSet.size > 0;
   return (feature) => {
@@ -165,12 +165,12 @@ function districtStyle(selectedSet) {
     const excluded = showShading && !selectedSet.has(name);
     return {
       stroke: excluded,
-      color: "#c89318",
+      color: "#c84545",
       weight: 1,
-      opacity: 0.55,
+      opacity: 0.6,
       fill: excluded,
-      fillColor: "#fde68a",
-      fillOpacity: 0.35,
+      fillColor: "#fca5a5",
+      fillOpacity: 0.3,
     };
   };
 }
@@ -217,6 +217,9 @@ function buildMap(el) {
     touchZoom: false,
     keyboard: false,
   }).setView(BERLIN_CENTER, BERLIN_ZOOM);
+  // Drop the "Leaflet" prefix — not legally required. OSM (ODbL) and CARTO's
+  // basemap terms both REQUIRE attribution, so those credits stay.
+  mapInstance.attributionControl.setPrefix(false);
   // CartoDB Voyager — clean, Google-Maps-ish base style.
   L.tileLayer("https://{s}.basemaps.cartocdn.com/rastertiles/voyager/{z}/{x}/{y}{r}.png", {
     attribution: "© OpenStreetMap · © CARTO",