create-a-container: Remove shell-based mail command

[runleveldev]

Issue: Replace shell-based mail command with native Node.js email library

Description:
The current implementation sends email using a shell command:

const mailCmd = `echo "${details}" | mail -r accounts@opensource.mieweb.org -s "New Intern Account Request" devopsalerts@mieweb.com`;

This approach relies on system utilities and shell execution, which introduces potential security and reliability issues.

Recommendation:
Use a Node.js email library such as [nodemailer](https://www.npmjs.com/package/nodemailer) to send emails directly within the application.

Benefits:

• Avoids shell injection and command execution risks
• Works across platforms without relying on system mail utilities
• Provides structured error handling and better logging
• Easier to extend for HTML templates, attachments, or SMTP authentication

[runleveldev]

Will fix https://github.com/mieweb/opensource-server/security/code-scanning/16

[runleveldev]

This is removed by #136, but will need reimplemented. Will make a seperate issue to reimplement account email confirmation.