fix(mail/delivery): Centralize runtime/plugin imports and switch modules to use plugins exports; unify EventEmitter usage; update Deno dependencies and small path/server refactors

ts/mail/delivery/placeholder.ts

@@ -6,3 +6,9 @@
 export class DeliveryPlaceholder {
   // Placeholder for delivery functionality
 }
+
+export class SmtpServer {
+  // Placeholder SMTP server
+  async start() {}
+  async stop() {}
+}