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/Pagination.svelte

@@ -60,7 +60,7 @@
     <div class="flex items-center">
       {#if hasPrev}
         <a href={pageHref(prevPage)} class="{baseShape} {navShape} {inactiveColors}" aria-label={t(T.pagination_prev)}>
-          <Icon icon="mdi:chevron-left" class="size-4" aria-hidden="true" />
+          <Icon icon="lucide:chevron-left" class="size-4" aria-hidden="true" />
           <span class="hidden sm:inline">{t(T.pagination_prev)}</span>
         </a>
       {/if}
@@ -76,7 +76,7 @@
       {#if hasNext}
         <a href={pageHref(nextPage)} class="{baseShape} {navShape} {inactiveColors}" aria-label={t(T.pagination_next)}>
           <span class="hidden sm:inline">{t(T.pagination_next)}</span>
-          <Icon icon="mdi:chevron-right" class="size-4" aria-hidden="true" />
+          <Icon icon="lucide:chevron-right" class="size-4" aria-hidden="true" />
         </a>
       {/if}
     </div>