Mark one inbox item read

Resolves one inbox row, and what that MEANS depends on the row’s kind (R8-07). A mention is resolved outright — nothing else ever closes one, so reading it is finishing it: the row becomes done and leaves the default status=open listing and the badge. An approval, a task or a parked row becomes read and STAYS open — it is still the caller’s blocking work, and only the work behind it closing resolves it. A connector row is neither: it is dismissed until the connection FAILS A CHECK again, at which point it comes back unread — the breakage, not the reading, owns its lifetime. Authorization: the API verifies the personal recipient or fresh shared-space read access, including task assignment, before relaying the write. Another user’s personal row and inaccessible shared rows return 404. itemId is the row id both readers publish (id here, itemId on GET /api/me/work) or, for a connector row, the connection id. A refId is NOT accepted: it names the approval / task / question, which repeats across sessions, so it can never identify one row.