Add a member to a workspace using an invite code

Adds a member to the workspace using a short-lived invite code generated by GET /v2/workspaces/members/code. The invited user is identified by the user ID embedded in the code; the caller specifies the member's role (view, manager, maintain, admin).

Up to the plan's per-workspace member cap. The workspace owner cannot be invited to their own workspace.

Rate limited to 1 addition every 5s per user.