Deactivate and Reactivate admin accounts (Stretch)

[SamNie2027]

Summary
Implement the ability to deactivate and reactivate admin accounts. This ensures that users who no longer hold admin roles do not retain access, while allowing accounts to be restored when needed.

Currently, there is no way to revoke admin access, which poses a risk when roles change. This feature ensures proper access control and account lifecycle management while working within the existing Cognito-based authentication setup.

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Acceptance Criteria

• Admins can deactivate their own accounts
• Deactivated admins can no longer log in
• Deactivation is implemented using Cognito-compatible flows (frontend-triggered where applicable)
• Deactivated admins can regain access through a verified email-based flow (Cognito)
• System maintains integrity of existing data associated with deactivated admins
• Remember to update tests on the backend. Frontend tests are optional.