v1.27.0 — Option to start clips further into the song

Start clips further into the song

Some music opens with a long instrumental before anyone sings, which makes a five-second clip taken from the very beginning hard to place for the wrong reason.

Set CLIP_START_S=30 to start every clip 30 seconds in instead. It is off by default, so nothing changes unless you turn it on.

• It is a floor over the existing silence detection — a song whose audible start is detected later still uses the later one.
• The reveal's payoff clip moves along with it.
• Short songs are clamped so the 20-second clip still fits.
• It is library-wide rather than a per-game option, because clips are cut ahead of time.

Because it applies when clips are cut, turning it on for a library that already has clips means re-cutting — but nothing goes offline while that happens. Tracks cut at a different setting are queued behind anything still waiting for its first clips, and keep their existing clips until each one is replaced. The nightly cut converts the library over the following sessions; a single POST /api/clips/cut?limit=20000 (or the Cut clips button on /admin) does it in one pass.

Also in this release: a re-cut that fails part-way no longer removes a playable track's existing clips, and a raised start can no longer cut past the end of a track whose duration isn't known.

See docs/setup.md for the details.