Make DNS servers fully dynamic from config.json

DNS server IDs (dns1, dns2, dns3) were hardcoded throughout the frontend
and backend. Now config.json's dnsServers object is the single source of
truth — adding or removing a DNS server in config automatically updates
the dashboard cards, credential modal, health checks, and probes.

- credentials.js: rebuild modal sections dynamically from SITE.dnsServers
- globals.js: add getPrimaryDnsId() helper for primary DNS lookups
- service-create.js, service-infrastructure.js: use dynamic DNS ID
- startup-validator.js: dynamic topCardServices from config
- middleware.js: add license endpoints to public routes

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

status/js/globals.js

@@ -85,6 +85,14 @@ function getDnsServerAddr(dnsId) {
   const s = SITE.dnsServers[dnsId];
   return s ? `${s.ip}:${s.port}` : buildDomain(dnsId);
 }
+/** Get the DNS ID whose IP matches the primary DNS config (dns.ip) */
+function getPrimaryDnsId() {
+  if (!SITE.dnsIp) return null;
+  for (const [id, info] of Object.entries(SITE.dnsServers)) {
+    if (info.ip === SITE.dnsIp) return id;
+  }
+  return null;
+}
 
 // ===== DYNAMIC DNS CARD RENDERER =====
 function renderDnsCards() {