Email validation regex is incorrect

[ChristianLempa]

The email validation regex in cli/core/variable.py line 12 is malformed:

EMAIL_REGEX = re.compile(r"^[^@\\s]+@[^@\\s]+\\.[^@\\s]+$")

The double backslashes are causing it to match literal backslash-s characters instead of whitespace. It should be:

EMAIL_REGEX = re.compile(r"^[^@\s]+@[^@\s]+\.[^@\s]+$")

This causes email validation to fail for all valid email addresses like admin@example.com.

Steps to reproduce:

1. Create a template with an email type variable with default admin@example.com
2. Run compose validate
3. Validation fails with "value must be a valid email address"

Expected behavior:
Standard email addresses should pass validation.

[ChristianLempa]

Updated Approach

The current regex-based email validation is fundamentally flawed. Email addresses follow RFC 5322/5321, which is too complex for regex to handle properly. Valid addresses like "John Doe"@example.com, user+tag@example.com, or user@[192.168.1.1] will fail simple regex patterns.

Proposed Solution

Replace regex validation with proper RFC-compliant email validation using the email-validator library. This provides:

• RFC 5321/5322 compliant validation
• Handles complex cases (quoted strings, IPv6 literals, internationalized domains)
• Industry-standard solution
• Better error messages for invalid emails

Implementation Plan

1. Add email-validator dependency to pyproject.toml
2. Replace EMAIL_REGEX with validate_email() from email-validator
3. Update _convert_email() method to use the library
4. Update tests if needed

This will ensure robust, standards-compliant email validation.