Initial commit: DNS Test - DNS health checking tool

Go backend (miekg/dns) + Nuxt 3 frontend (Tailwind CSS v4).

8 check categories, 52 checks total:
- Overview: @ record, WWW, MX with ASN/provider lookup
- Domain Registration: expiry, registrar (RDAP + whois fallback)
- Parent Delegation: NS records, glue, consistency
- Nameservers: 17 checks (reachability, auth, recursion, TCP/UDP, AXFR, etc.)
- SOA: serial consistency, timing values
- Mail (MX): 11 checks (CNAME, PTR, public IPs, consistency)
- Mail Auth: SPF, DKIM, DMARC
- WWW: A record, CNAME

Features:
- SSE streaming (results appear as each category completes)
- SQLite history (modernc.org/sqlite)
- Rate limiting, CORS, request logging
- Dark mode, responsive design

frontend/app/components/LoadingSpinner.vue

@@ -0,0 +1,14 @@
+<template>
+  <div class="flex flex-col items-center justify-center py-20">
+    <div class="relative h-16 w-16">
+      <div class="absolute inset-0 rounded-full border-4 border-gray-200 dark:border-gray-700"></div>
+      <div class="absolute inset-0 animate-spin rounded-full border-4 border-transparent border-t-indigo-600 dark:border-t-indigo-400"></div>
+    </div>
+    <p class="mt-6 text-lg font-medium text-gray-600 dark:text-gray-400">
+      Checking DNS configuration...
+    </p>
+    <p class="mt-1 text-sm text-gray-400 dark:text-gray-500">
+      This may take a few seconds
+    </p>
+  </div>
+</template>