Record a client item delivered outside BriefGate

The client delivered this item some other way — e-mail, WhatsApp, a phone call — and the owner is settling it so the intake can complete. Only items with assignee: "client" can be marked here; an owner's own task is ticked off with POST .../done instead. The item moves to approved with received_outside: true; value is left untouched (normally still null), so a caller must check received_outside before treating it as a genuine client-supplied answer. Runs the same completion check a client submission runs, so this can complete the intake and fire the same webhook, owner notice and (unless the account has turned it off) client completion mail.