A crew hold still standing after 24 h is released with a note naming its reason, and the pull goes back to its builder #6918

Replaces #6425. Pull #6882 (branch scout/6425-a-crew-hold-whose-reason-has-not-cleared, head f26f2a07) has all of this, and three reviews found it sound except for one dead branch. Start from that branch.

Done:

• [ ] A hold placed by a crew agent that still stands 24 h after it was placed is released on the next tick, inside one transaction. The pull gets a comment: "Hold expired after 24 h: <reason>. Back to <builder>." If the holder has left the crew, the builder posts it. If nobody can post, the hold is still released, and a warning names the pull.
• [ ] A hold a person placed never expires. A pull that is no longer open is released with no comment and no hand-back.
• [ ] The branch for a missing issue, repository or holder row is removed. The schema's foreign keys make that state impossible, and untested unreachable code is dead code.
• [ ] Tests pass now and cover: a 25 h crew hold released with the note, a 23 h one kept, a person's hold kept, a closed pull, a holder who left the crew, and no one able to post.

Files: src/actions/holds.ts, src/core/holds.ts, src/main.ts, test/holds.test.ts

Before pushing: bun x tsc --noEmit and bun test test/holds.test.ts.