Make email service initialization asynchronous

Convert getEmailService() to async function and update all callers to use await.
Replace synchronous require() with dynamic import() for admin-config module.
Add SMTP config loading to admin configuration dialog.

server/api/auth/send-verification-email.post.ts

@@ -82,7 +82,7 @@ export default defineEventHandler(async (event) => {
 
     // Send verification email
     const { getEmailService } = await import('~/server/utils/email');
-    const emailService = getEmailService();
+      const emailService = await getEmailService();
 
     try {
       await emailService.sendWelcomeEmail(email, {