feat(email-domains): support creating email domains on optional subdomains

ts/email/classes.email-domain.manager.ts

@@ -48,6 +48,7 @@ export class EmailDomainManager {
 
   public async createEmailDomain(opts: {
     linkedDomainId: string;
+    subdomain?: string;
     dkimSelector?: string;
     dkimKeySize?: number;
     rotateKeys?: boolean;
@@ -58,7 +59,9 @@ export class EmailDomainManager {
     if (!domainDoc) {
       throw new Error(`DNS domain not found: ${opts.linkedDomainId}`);
     }
-    const domainName = domainDoc.name;
+    const baseDomain = domainDoc.name;
+    const subdomain = opts.subdomain?.trim() || undefined;
+    const domainName = subdomain ? `${subdomain}.${baseDomain}` : baseDomain;
 
     // Check for duplicates
     const existing = await EmailDomainDoc.findByDomain(domainName);
@@ -90,6 +93,7 @@ export class EmailDomainManager {
     doc.id = plugins.smartunique.shortId();
     doc.domain = domainName.toLowerCase();
     doc.linkedDomainId = opts.linkedDomainId;
+    doc.subdomain = subdomain;
     doc.dkim = {
       selector,
       keySize,
@@ -306,6 +310,7 @@ export class EmailDomainManager {
       id: doc.id,
       domain: doc.domain,
       linkedDomainId: doc.linkedDomainId,
+      subdomain: doc.subdomain,
       dkim: doc.dkim,
       rateLimits: doc.rateLimits,
       dnsStatus: doc.dnsStatus,