feat: Add local Nodemailer fallback for development email service

[karthik768990]

Summary

This PR introduces a local Nodemailer fallback for sending emails in development.
It removes the dependency on SendGrid API keys for local testing and simplifies user/admin creation workflows.

Problem

Currently, developers must configure SendGrid API keys even for local development, which blocks setup.

Solution

• Added a Nodemailer-based local email service (emailServiceNodemailer.js)
• Updated emailService.js to select between SendGrid (production) and Nodemailer (local) using the EMAIL_SERVICE environment variable.
• Local .env file can be used for Gmail credentials for Nodemailer.

Testing

1. Create a .env file in shopping-server with:
   EMAIL_SERVICE=nodemailer
   VENIQA_NODEMAILER_USER=<your_gmail>
   VENIQA_NODEMAILER_PASSWORD=<app_password>
2. Run npm run dev.
3. Create a new user/admin → confirmation email should be sent via Gmail.

Notes

• .env should never be committed; add it to .gitignore.
• Default behavior for production (SendGrid) remains unchanged.
• Simplifies onboarding for new developers.

###Comment: I haven't included the .env as it contains some sensitive information and the developers should create their own .env files