- Fail the run when the connection drops while a sync is running, and clear
the active conflict, so the queue is not sent on a dead client and a
re-login as another account never receives this profile's uploads.
- Backfill last_modified from upload_time in the 37 -> 38 migration and drop
the "last_modified is null" arm from the sync-check query, so rows that
predate the column stop reporting as changed on every poll.
- Skip conflicts during auto runs and report how many were skipped, instead
of opening the modal conflict dialog from a timer or a file-watcher event.
