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/js/setup-wizard.js

@@ -174,8 +174,9 @@ window.populateTimezoneSelect = function(selectEl, selectedTz) {
     if (currentConfigType === 'homelab') {
       config.tld = document.getElementById('setup-tld')?.value?.trim() || '.home';
       config.caName = document.getElementById('setup-ca-name')?.value?.trim() || '';
+      const selectedProvider = document.getElementById('setup-dns-provider')?.value || 'technitium';
       config.dns = {
-        provider: 'technitium',
+        provider: selectedProvider,
         ip: document.getElementById('setup-dns-ip')?.value?.trim() || '',
         port: document.getElementById('setup-dns-port')?.value?.trim() || DC.DEFAULTS.DNS_PORT,
         token: document.getElementById('setup-dns-token')?.value?.trim() || ''