The steward's hold on a red pull is marked as a red hold, so it releases itself when that head goes green #6831

Follow-up the reviewer of #6357 asked for: after #6348, only the MCP tool passes forRed, so the stale "red alone, held" holds that prompted #5930 stay.

Done:

• [ ] Where the forge itself holds a pull because its check is red (the steward or landing pass), it places the hold with forRed and the head it was red on.
• [ ] A test: the forge holds a red pull, a green check lands on the same head, the sweep releases it; a person's hold on the same pull is never released.
• [ ] A hold placed through PUT …/pulls/:n/hold, the studio or the tty stays a person's hold.

Files: the steward's hold call site (src/crew/), test/red-hold-steward.test.ts. Suggested: scout.

Dropped, with #6847: the forge itself places no hold on a red pull, so there is no placer to mark. A red pull is held by a person, who can say until: "green" (MCP hold, the API, the form) and get the release on green from #6508.