What does this PR do?

This PR enables inviting users by email directly from the Team Event-Type “Assignment” selector.

Previously, only existing team members could be selected.
With this change:

• Users can type email addresses directly into the assignment dropdown
• If the email does not belong to an existing team member:
  • The user is automatically invited to the team as a Member
• Supports multiple comma-separated emails:
  • user1@example.com, user2@example.com
• Prevents duplicate invites
• Validates email format before submission

This improves onboarding flow and removes friction when assigning new team members to event-types.

• Fixes #13532
• Fixes CAL-3076

Visual Demo

Before

• Assignment dropdown only allowed selecting existing team members.
• New users had to be manually added to the team first.

After

• Email can be typed directly.
• Non-team email triggers automatic invite.
• Multiple emails supported (comma separated).
• Clean validation and no duplicate invite behavior.

📹 Demo video attached (shows:

1. Entering single email
2. Entering multiple emails
3. Auto invite behavior
4. Assignment success)

Mandatory Tasks

• I have self-reviewed the code.
• I have updated developer docs if required (N/A).
• Automated tests added/updated to cover:
  • Email parsing
  • Multiple email handling
  • Invite creation
  • Duplicate prevention

How should this be tested?

1. Go to Team → Event Type → Assignment.
2. Type a valid email that is NOT part of the team.
3. Save changes.
4. Verify:
   • Invite is sent
   • User added as Member
   • Assignment saved successfully

Test multiple emails: /claim #13532