feat(windkarte): permanente 2km/5km-Ringe togglebar in Legende

Zeigt 2km (indigo) und 5km (lila) Pufferringe für alle Gebiete gleichzeitig,
unabhängig von Selektion. Default versteckt, Klick auf Legendenitem ein-/ausblenden.

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

src/lib/components/blocks/WindkarteBlock.svelte

@@ -22,6 +22,7 @@ let areas = $state<WindArea[]>([]);
   let initialGebietsNr = $state<string | null>(null);
   let resetMap: (() => void) | null = null;
   let hiddenStatuses = $state<string[]>([]);
+  let hiddenRings = $state<string[]>(["2km", "5km"]);
 
   function toggleStatus(status: string) {
     hiddenStatuses = hiddenStatuses.includes(status)
@@ -29,6 +30,12 @@ let areas = $state<WindArea[]>([]);
       : [...hiddenStatuses, status];
   }
 
+  function toggleRing(ring: string) {
+    hiddenRings = hiddenRings.includes(ring)
+      ? hiddenRings.filter((r) => r !== ring)
+      : [...hiddenRings, ring];
+  }
+
   const MapComponent = browser
     ? import("$lib/components/WindkarteMap.svelte").then((m) => m.default)
     : null;
@@ -113,6 +120,7 @@ let areas = $state<WindArea[]>([]);
           {areas}
           {initialGebietsNr}
           {hiddenStatuses}
+          {hiddenRings}
           onselect={handleSelect}
           onready={(ctrl) => { resetMap = ctrl.reset; }}
         />
@@ -159,6 +167,18 @@ let areas = $state<WindArea[]>([]);
           {ring.label}
         </span>
       {/each}
+      {#each [{ key: "2km", color: "#5e6fa3", label: "2 km" }, { key: "5km", color: "#8a567a", label: "5 km" }] as ring}
+        <button
+          type="button"
+          onclick={() => toggleRing(ring.key)}
+          class="flex items-center gap-1.5 cursor-pointer select-none transition-opacity
+                 {hiddenRings.includes(ring.key) ? 'opacity-35' : 'opacity-100'}"
+          title={hiddenRings.includes(ring.key) ? 'Einblenden (alle Gebiete)' : 'Ausblenden'}
+        >
+          <span class="dashed-line {hiddenRings.includes(ring.key) ? 'opacity-40' : ''}" style="border-color:{ring.color}"></span>
+          <span class="{hiddenRings.includes(ring.key) ? 'line-through' : ''}">{ring.label}</span>
+        </button>
+      {/each}
     </span>
   </div>
 </div>