feat(header): icon nav redesign + migrate icons mdi→lucide

- Header desktop nav: social icons grouped in a wald-tinted pill with
  labels, active-state (aria-current + bold), opacity hover (no per-item bg)
- Mobile overlay: social links as icon+label rows with active-state
- Search button: lucide:search, icon-only
- Migrate all icons mdi→lucide app-wide (234 refs); brand/language logos
  (google, whatsapp, mastodon, telegram, language-*) stay on mdi
- generate-icons: emit mdi + lucide subsets; add @iconify-json/lucide
- iconify-offline: register lucide collection
- scripts/icon-map|validate|apply: reusable migration tooling

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/lib/components/blocks/OrganisationsMapBlock.svelte

@@ -144,7 +144,7 @@
         aria-label="Karte aktivieren"
       >
         <span class="flex items-center gap-2 rounded-md bg-white/95 px-3 py-1.5 text-sm font-medium text-stein-800 shadow-md">
-          <Icon icon="mdi:cursor-default-click-outline" class="size-4" />
+          <Icon icon="lucide:mouse-pointer-click" class="size-4" />
           Karte aktivieren
         </span>
       </button>
@@ -167,13 +167,13 @@
               class="shrink-0 text-stein-400 transition-colors hover:text-stein-700"
               aria-label="Schließen"
             >
-              <Icon icon="mdi:close" class="size-4" />
+              <Icon icon="lucide:x" class="size-4" />
             </button>
           </div>
 
           {#if selectedOrg.location?.text}
             <p class="mb-3 flex items-center gap-1 text-xs text-stein-500">
-              <Icon icon="mdi:map-marker-outline" class="size-3.5 shrink-0" />
+              <Icon icon="lucide:map-pin" class="size-3.5 shrink-0" />
               {selectedOrg.location.text}
             </p>
           {/if}
@@ -203,13 +203,13 @@
                   {/if}
                   {#if c.email}
                     <a href="mailto:{c.email}" class="mt-0.5 flex items-center gap-1 text-wald-700 hover:underline">
-                      <Icon icon="mdi:email-outline" class="size-3 shrink-0" />
+                      <Icon icon="lucide:mail" class="size-3 shrink-0" />
                       <span class="truncate">{c.email}</span>
                     </a>
                   {/if}
                   {#if c.phone}
                     <a href="tel:{c.phone.replace(/\s+/g, '')}" class="mt-0.5 flex items-center gap-1 text-wald-700 hover:underline">
-                      <Icon icon="mdi:phone" class="size-3 shrink-0" />
+                      <Icon icon="lucide:phone" class="size-3 shrink-0" />
                       {c.phone}
                     </a>
                   {/if}
@@ -228,7 +228,7 @@
               rel="noopener noreferrer"
               class="btn-outline btn-sm w-full justify-center no-underline!"
             >
-              <Icon icon="mdi:open-in-new" class="size-3.5" />
+              <Icon icon="lucide:external-link" class="size-3.5" />
               {getLinkLabel(selectedOrg)}
             </a>
           {/if}