refactor: migrate services from app.config to unified config

- Update email verification template to use unifiedConfig
- Update ProductionDatabaseStrategy to use databaseConfig from unified config
- Update mailgun service to use unifiedConfig for baseUrl
- Provides consistent configuration access across all services
- Part of migration to single source of truth configuration system

services/mailgun.service.ts

@@ -4,7 +4,7 @@
  */
 
 import { getMailgunConfig, type MailgunConfig } from './mailgun.config';
-import { appConfig } from '../config/app.config';
+import { unifiedConfig } from '../config/unified.config';
 
 interface EmailTemplate {
   subject: string;
@@ -139,13 +139,13 @@ export class MailgunService {
   }
 
   async sendVerificationEmail(email: string, token: string): Promise<boolean> {
-    const verificationUrl = `${appConfig.baseUrl}/verify-email?token=${token}`;
+    const verificationUrl = `${unifiedConfig.app.baseUrl}/verify-email?token=${token}`;
     const template = this.getVerificationEmailTemplate(verificationUrl);
     return this.sendEmail(email, template);
   }
 
   async sendPasswordResetEmail(email: string, token: string): Promise<boolean> {
-    const resetUrl = `${appConfig.baseUrl}/reset-password?token=${token}`;
+    const resetUrl = `${unifiedConfig.app.baseUrl}/reset-password?token=${token}`;
     const template = this.getPasswordResetEmailTemplate(resetUrl);
     return this.sendEmail(email, template);
   }