The Electron updater copied state.db to state.db.pre-update-emergency-*.bak on every
update hand-off regardless of updates.pre_update_backup, pinning ~3x state.db on disk.
preflightStateDb now asks the backend (`hermes config get updates.pre_update_backup --json`)
and skips the emergency copy when the mode is off/false/none/disabled; any probe failure
fails open to taking the backup.
Squashed from PR #116755 (4 commits) for a clean apply onto origin/main.
4de06d1dbf