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>

scripts/icon-validate.mjs

@@ -0,0 +1,33 @@
+import { MAP, KEEP_MDI } from './icon-map.mjs';
+import fs from 'node:fs';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+
+const ROOT = path.resolve(path.dirname(fileURLToPath(import.meta.url)), '..');
+const lucide = JSON.parse(
+  fs.readFileSync(path.join(ROOT, 'node_modules/@iconify-json/lucide/icons.json'), 'utf8'),
+);
+const has = (n) => Boolean(lucide.icons[n] || (lucide.aliases && lucide.aliases[n]));
+
+const all = fs
+  .readFileSync(process.env.TMPDIR + '/mdi_all.txt', 'utf8')
+  .trim()
+  .split('\n')
+  .map((s) => s.replace('mdi:', ''));
+const cms = ['cloud', 'email', 'facebook', 'map', 'video', 'whatsapp', 'youtube'];
+const set = [...new Set([...all, ...cms])].sort();
+
+const bad = [];
+const unmapped = [];
+for (const m of set) {
+  if (KEEP_MDI.has(m)) continue;
+  const l = MAP[m];
+  if (l === undefined) {
+    unmapped.push(m);
+    continue;
+  }
+  if (has(l) === false) bad.push(`${m} -> lucide:${l}`);
+}
+console.log('total mdi:', set.length, '| keep-mdi:', [...KEEP_MDI].filter((k) => set.includes(k)).length);
+console.log('UNMAPPED:', unmapped.length ? unmapped.join(', ') : 'none');
+console.log('INVALID lucide names:', bad.length ? '\n  ' + bad.join('\n  ') : 'none');