fix(dns): register separate handlers for each DNS record to serve multiple records

The previous implementation grouped records by domain and only returned the first
matching record. This prevented serving multiple NS records for a domain, which
caused GoDaddy to reject the nameservers.

Changes:
- Modified registerDnsRecords to register a separate handler for each record
- This works around smartdns limitation where it breaks after first handler match
- Now all NS records are properly served in DNS responses
- Added readme.smartdns.md documenting the underlying issue in smartdns module

The root cause is in smartdns DnsServer which breaks after finding the first
matching handler, preventing multiple records of the same type from being served.

ts/classes.dcrouter.ts

@@ -693,40 +693,27 @@ export class DcRouter {
   private registerDnsRecords(records: Array<{name: string; type: string; value: string; ttl?: number}>): void {
     if (!this.dnsServer) return;
     
-    // Group records by domain pattern
-    const recordsByDomain = new Map<string, typeof records>();
-    
+    // Register a separate handler for each record
+    // This ensures multiple records of the same type (like NS records) are all served
     for (const record of records) {
-      // Use exact domain name for registration - no automatic wildcard prefix
-      const pattern = record.name;
-      if (!recordsByDomain.has(pattern)) {
-        recordsByDomain.set(pattern, []);
-      }
-      recordsByDomain.get(pattern)!.push(record);
-    }
-    
-    // Register handlers for each domain pattern
-    for (const [domainPattern, domainRecords] of recordsByDomain) {
-      const recordTypes = [...new Set(domainRecords.map(r => r.type))];
-      
-      this.dnsServer.registerHandler(domainPattern, recordTypes, (question) => {
-        const matchingRecord = domainRecords.find(
-          r => r.name === question.name && r.type === question.type
-        );
-        
-        if (matchingRecord) {
+      // Register handler for this specific record
+      this.dnsServer.registerHandler(record.name, [record.type], (question) => {
+        // Check if this handler matches the question
+        if (question.name === record.name && question.type === record.type) {
           return {
-            name: matchingRecord.name,
-            type: matchingRecord.type,
+            name: record.name,
+            type: record.type,
             class: 'IN',
-            ttl: matchingRecord.ttl || 300,
-            data: this.parseDnsRecordData(matchingRecord.type, matchingRecord.value)
+            ttl: record.ttl || 300,
+            data: this.parseDnsRecordData(record.type, record.value)
           };
         }
         
         return null;
       });
     }
+    
+    logger.log('info', `Registered ${records.length} DNS handlers (one per record)`);
   }
   
   /**