Function would_orphan_developers 

pub async fn would_orphan_developers(
    db: &Db,
    user_id: i64,
    new_role: Option<Role>,
) -> Result<bool>

Phase 7a/0.5/f — would the proposed change leave the system with zero active Developers?

new_role:

• None → user is being deleted entirely.
• Some(role) → user’s role is being changed to role.

Returns true only when:

• exactly one active Developer exists, AND
• the target user IS that Developer, AND
• the action would remove their Developer status (deletion or demotion to anything other than Developer).

Used as a server-side guard in do_user_edit and do_user_delete, and as a CLI warning before destructive role changes.