fix(sqlite): tag per-migration database backups with version and prevent collisions - #3785

By creating this pull request, I grant the project maintainers an unlimited, perpetual license to use, modify, and redistribute these contributions under any terms they choose, including both the AGPLv3 and the Fossorial Commercial license terms. I represent that I have the right to grant this license for all contributed content.

Fixes the remaining half of #3761 (the timestamp naming was fixed by #3769; this covers the duplicate backups).

Root cause

In \server/setup/migrationsSqlite.ts, \executeScripts()\ called \�ackupDb()\ inside the per-migration loop, so upgrading across N versions produced N backups, one before each migration. Each later backup contains the earlier migrations' changes, so none of them is a clean pre-upgrade restore point (and when two migrations run within the same second, the second backup silently overwrites the first under the identical timestamped name).

Fix

Take one backup before any pending migration runs. Skipped when there is nothing to run or \DISABLE_BACKUP_ON_MIGRATION\ is set, same as before. The Postgres path never took per-migration backups, so no change was needed there.

Verification (Docker, node:24.18.1-bookworm, matching CI)

Seeded a scratch sqlite db at version 1.21.0 (pending: 1.22.0, 1.23.0) and ran the real \server/setup/migrationsSqlite.ts:

• Before: surviving backup held mid-upgrade state (\sites\ had \exitNodeSubnet, versions 1.21.0+1.22.0 recorded); new \server/setup/migrationsSqlite.backup.test.ts\ fails on unpatched code with exit 1.
• After: exactly one backup holding the true pre-upgrade snapshot (\sites.subnet, only 1.21.0 recorded); new test passes with exit 0.
• \ sc --noEmit\ exit 0; \prettier --check\ on both touched files exit 0; existing \server/lib/backupFileName.test.ts\ passes.
• Note: \eslint\ cannot run in this tree at all right now (typescript-eslint does not support the repo's TS 7.0, fails identically on untouched files; fix(deps): revert typescript 7.0.2 -> 6.0.3 to fix broken ESLint #3773 tracks that separately).

Run the new test with:
px tsx server/setup/migrationsSqlite.backup.test.ts\ (after
pm ci,
pm run set:sqlite,
pm run set:oss).