Add last login time to Collaborator accounts

🔍 Problem Statement

Pelcro does not track or display when a collaborator last logged in. Admins have no visibility into account activity, making it difficult to identify stale accounts or enforce security policies.

💡 User Story

As an Account Owner, I want to see the last login time for each collaborator, so that I can identify inactive accounts and maintain security hygiene.

🎯 Definition of Done (DoD)

A feature is done when:

✔️ Given the collaborator list, when an Account Owner views it, then each collaborator's last login timestamp is displayed — and the data is available via the API.