Change Neon organization member's role

Change a joined member's role on the current Neon organization, identified by email. Free-text role matched case-insensitively against Neon's role picker (Admin, Member). Only applies to already-Joined members -- pending invites don't expose a role-change control (their role is set at invite time; cancel and re-invite with a different role instead). If the member's role already matches the requested role, this is a no-op (Neon's own menu doesn't fire a confirm dialog or API call for a same-role click) and returns changed:false. Returns the member's email, resulting role, and whether a change occurred.