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)

dashcaddy-api/dns-providers/base.js

@@ -0,0 +1,69 @@
+/**
+ * Base DNS Provider Adapter
+ * All DNS provider adapters must extend this class and implement the required methods.
+ * 
+ * Each adapter handles the specifics of talking to a particular DNS provider's API.
+ * The routes layer calls these methods generically — no provider-specific logic in routes.
+ */
+class BaseDNSProvider {
+  constructor(config, ctx) {
+    this.config = config;    // Provider-specific config (api token, server url, etc.)
+    this.ctx = ctx;          // Shared app context (log, credentialManager, fetchT, etc.)
+    this.providerId = 'base';
+    this.displayName = 'Base DNS Provider';
+  }
+
+  /** Check if this provider supports a given capability */
+  supportsCapability(cap) {
+    // Capabilities: 'create-record', 'delete-record', 'resolve', 'list-records',
+    //              'logs', 'restart', 'update-check', 'credentials', 'zones'
+    return false;
+  }
+
+  /** Authenticate and return a token/session */
+  async authenticate() { throw new Error('Not implemented'); }
+
+  /** Create a DNS record */
+  async createRecord({ domain, zone, type, value, ttl, overwrite }) { throw new Error('Not implemented'); }
+
+  /** Delete a DNS record */
+  async deleteRecord({ domain, type, value }) { throw new Error('Not implemented'); }
+
+  /** Resolve/query existing records for a domain */
+  async resolveRecords({ domain, zone, type }) { throw new Error('Not implemented'); }
+
+  /** List all records in a zone */
+  async listRecords({ zone }) { throw new Error('Not implemented'); }
+
+  /** Get DNS query logs */
+  async getLogs({ limit, server }) { throw new Error('Not implemented'); }
+
+  /** Restart the DNS server */
+  async restartServer({ server }) { throw new Error('Not implemented'); }
+
+  /** Check for DNS server updates */
+  async checkUpdate({ server }) { throw new Error('Not implemented'); }
+
+  /** Get provider status info */
+  async getStatus() {
+    return {
+      providerId: this.providerId,
+      displayName: this.displayName,
+      capabilities: this.getCapabilities(),
+      authenticated: false
+    };
+  }
+
+  /** Get list of supported capabilities */
+  getCapabilities() {
+    return [];
+  }
+
+  /** Validate provider-specific config */
+  validateConfig() { return { valid: true, errors: [] }; }
+
+  /** Clean up resources on shutdown */
+  async shutdown() {}
+}
+
+module.exports = BaseDNSProvider;