feat: DNS provider abstraction — Technitium, Cloudflare, RFC 2136, Manual

- dns-providers/: adapter base class + registry with auto-discovery
- technitium.js: wraps existing Technitium API calls into adapter interface
- cloudflare.js: Cloudflare API v4 adapter (zones, records, credentials)
- rfc2136.js: RFC 2136 dynamic DNS via nsupdate (BIND, PowerDNS, etc.)
- manual.js: no-op adapter for external DNS management with instructions
- provider-dns.js: provider-aware DNS context, resolves active adapter from config
- Universal helper methods: universalCreateRecord/Delete/ResolveRecord
- All 7 route files updated to use universal methods instead of raw dns.call()
- Setup wizard: provider dropdown (Technitium, Cloudflare, RFC 2136, Manual)
- DNS template selector: added Cloudflare and External/Manual options
- Config schema: validates dns.provider field
- Capability gating on Technitium-specific endpoints (logs, restart, update)
- Backward compatible: no provider set = auto-detect (technitium if dns.ip exists)

status/index.html

@@ -393,8 +393,14 @@
           <!-- DNS Server Configuration -->
           <div>
             <label class="form-label-accent">
-              🗂️ DNS Server (Technitium)
+              🗂️ DNS Provider
             </label>
+            <select id="setup-dns-provider" class="form-input-lg" style="margin-bottom: 12px;">
+              <option value="technitium">Technitium DNS (recommended)</option>
+              <option value="cloudflare">Cloudflare DNS</option>
+              <option value="rfc2136">RFC 2136 (BIND / PowerDNS / other)</option>
+              <option value="manual">Manual / External DNS</option>
+            </select>
             <div style="display: grid; grid-template-columns: 1fr auto; gap: 8px;">
               <input type="text" id="setup-dns-ip" value="" placeholder="DNS server IP"
                      style="padding: 12px; background: var(--card-bg); color: var(--fg); border: 1px solid var(--border); border-radius: 6px; font-size: 1rem;" />
@@ -409,7 +415,7 @@
           <!-- DNS Admin Token -->
           <div>
             <label class="form-label-accent">
-              🔑 Technitium Admin Token
+              🔑 DNS Admin Token / API Key
             </label>
             <input type="password" id="setup-dns-token" placeholder="Paste your admin token here"
                    class="form-input-lg" />