fix(database): slow migrations block startup with no feedback

[wizzomafizzo]

Summary

A slow database migration blocks service startup and reports nothing while it runs. On a MiSTer with a 229k-item library the service was unavailable for 2m14s with no output between "opening databases" and goose's completion line.

What the log showed

20:04:18  opening databases
20:04:18  effective database pragmas   db=user
20:04:18  goose: no migrations to run. current version: 20260818120000
20:04:19  created scheduled user database backup
20:04:19  effective database pragmas   db=media
          ... 2m13s of nothing ...
20:06:32  goose: successfully migrated database to version: 20260830140000

Why

Everything in pkg/database/migrations.go is logged at Debug: acquiring the mutex, setting the dialect, the filesystem, the logger. Debug logging is off by default, so a user sees none of it. The only Info line is goose's own, and it is emitted after the migration finishes — precisely when the feedback is no longer needed.

There is also no non-log channel at that point in startup: the API server is not listening yet, so no notification can be sent and nothing on a display can be updated.

Why it matters

Migrations are unbounded in cost and scale with library size, and MiSTer SD storage is roughly 680x slower than a desktop for index work — the same statement measured 198ms locally and 2m14s on the device. A migration that looks free in development can freeze startup for minutes in the field, and from the user's side it is indistinguishable from a hang.

The specific migration that caused this was fixed in #1371, but the gap is general: any future schema change on a large library hits it.

Worth considering

• An Info line naming each migration before it is applied, so the log shows what is being waited on.
• Some signal outside the log, since the API is not up yet — the platform display or the launcher are the only channels available that early.
• Whether unbounded table work in a migration should be allowed at all, or pushed to the indexing path where the cost is expected and already reported.