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/ContactCard.svelte

@@ -43,20 +43,20 @@
     onclick={() => downloadVCard(contact)}
     class="absolute top-3 right-3 text-stein-300 transition-colors hover:text-wald-600"
   >
-    <Icon icon="mdi:card-account-details-outline" class="size-4" />
+    <Icon icon="lucide:id-card" class="size-4" />
   </button>
 
   {#if contact.phone || contact.email}
     <div class="flex flex-col gap-1">
       {#if contact.phone}
         <a href="tel:{contact.phone.replace(/\s/g, '')}" class="inline-flex items-center gap-1.5 text-xs text-stein-600 no-underline hover:text-wald-700">
-          <Icon icon="mdi:phone-outline" class="size-3.5 shrink-0 text-stein-400" />
+          <Icon icon="lucide:phone" class="size-3.5 shrink-0 text-stein-400" />
           <span class="truncate">{contact.phone}</span>
         </a>
       {/if}
       {#if contact.email}
         <a href="mailto:{contact.email}" class="inline-flex items-center gap-1.5 text-xs text-stein-600 no-underline hover:text-wald-700">
-          <Icon icon="mdi:email-outline" class="size-3.5 shrink-0 text-stein-400" />
+          <Icon icon="lucide:mail" class="size-3.5 shrink-0 text-stein-400" />
           <span class="truncate">{contact.email}</span>
         </a>
       {/if}