Model multi-team membership separately from role

Represent team membership and role or organization policy as separate authority dimensions. A user may belong to several teams, while an organization-wide role may resolve to all teams and a narrowly scoped role may remain narrow despite extra membership rows.

Compute access from the explicit policy and the union of permitted team identifiers; do not assume team membership overrides role scope. Require explicit confirmation when adding a second team if that change is operationally significant.