fix: handle RFC-5322 email addresses with commas in display names

[samarth93]

Fixes #2302

Problem

Email validation was failing for RFC-5322 compliant addresses with commas in display names, like:

• "John, Doe" <[email protected]>

The issue occurred at multiple levels:

1. Email validation regex only validated bare addresses
2. Email splitting used naive split(",") which broke quoted display names

Solution

• Add extractEmailAddress() to parse the actual email from RFC-5322 format
• Add splitEmailAddresses() that respects commas inside quotes
• Update validateEmail() and validateEmailWithZod() to extract the email before validation
• Update MultiSelectInput.vue to use proper email splitting

Testing

1. Open any ticket and click Reply
2. Enter email: "John, Doe" <[email protected]>
3. Should be accepted without validation errors
4. Multiple emails like "John, Doe" <[email protected]>, [email protected] should split correctly