- GET /api/workspace/{id}/members — list all members with roles
- POST /api/workspace/{id}/members — invite user by email
- PUT /api/workspace/{id}/members/{user_id} — change role
- DELETE /api/workspace/{id}/members/{user_id} — remove member
- Roles: owner, admin, editor, viewer
- Uses existing workspace_members DB table (v2.0 schema)