The remove/role-change guards only protected the account owner, so a non-owner
admin could change their own role or remove themselves via a crafted request
(the UI hides it, but the backend didn't). Add an explicit self-guard to both
updateRole and removeMember.
Lock the whole role system with tests: accept assigns the exact invited role
(viewer/admin/member), invite requires and persists a role, updateRole supports
viewer and blocks self/owner/invalid, removeMember blocks self/owner, and a
viewer is read-only (view yes; create post / manage team / invite no).
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