Backup names were built inline from Date#getMonth, which is zero-indexed, so a
backup taken on 12 September 2026 was written as db_2026-8-12_20-35-56.sqlite.
No field was zero-padded either, giving names like db_2026-8-12_20-36-2.sqlite.
Extract formatBackupTimestamp into server/lib and use it from both places that
built the string: the backupDb helper in migrationsSqlite.ts and the inline copy
in the 1.0.0-beta9 setup script. Padding every field also makes the names sort
lexicographically in the order the backups were taken.
Adds tests covering both reported names, single-digit padding and sort order.
Reverting the helper to the old formula fails them with the exact name from the
report.
Hayyan Hajwani
9298ec7cdb