fix: NS cache lookup from authorities, UDP re-probe, shield alignment

- find_closest_ns checks authorities (not just answers) for NS records,
  fixing TLD priming cache misses that caused redundant root queries
- Periodic UDP re-probe every 5min when disabled — re-enables UDP
  after switching from a restrictive network to an open one
- Dashboard DNSSEC shield uses fixed-width container for alignment
- Blog post: tuck key-tag into trust anchor paragraph

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

site/dashboard.html

@@ -766,7 +766,7 @@ function applyLogFilter() {
       <td>${e.query_type}</td>
       <td class="domain-cell" title="${e.domain}">${e.domain}${allowBtn}</td>
       <td><span class="path-tag ${e.path}">${e.path}</span></td>
-      <td>${e.dnssec === 'secure' ? '<svg title="DNSSEC verified" width="12" height="12" viewBox="0 0 24 24" fill="none" stroke="var(--emerald)" stroke-width="2.5" stroke-linecap="round" stroke-linejoin="round" style="vertical-align:-1px;margin-right:3px;"><path d="M12 22s8-4 8-10V5l-8-3-8 3v7c0 6 8 10 8 10z"/><path d="m9 12 2 2 4-4"/></svg>' : ''}${e.rescode}</td>
+      <td style="white-space:nowrap;"><span style="display:inline-block;width:15px;text-align:center;">${e.dnssec === 'secure' ? '<svg title="DNSSEC verified" width="12" height="12" viewBox="0 0 24 24" fill="none" stroke="var(--emerald)" stroke-width="2.5" stroke-linecap="round" stroke-linejoin="round" style="vertical-align:-1px;"><path d="M12 22s8-4 8-10V5l-8-3-8 3v7c0 6 8 10 8 10z"/><path d="m9 12 2 2 4-4"/></svg>' : ''}</span>${e.rescode}</td>
       <td>${e.latency_ms.toFixed(1)}ms</td>
     </tr>`;
   }).join('');