Adds rows.Err() and Rows() open-failure logging in
computeSourceTotals so silent data drops surface in logs. Logs on
parseLastUsedString format misses for the same reason. Strengthens
the snapshot-survival test to assert LastUsed is a recent timestamp,
locking the SQLite time-string parser behaviour.
Refs: #9862
Signed-off-by: Ettore Di Giacinto <mudler@localai.io>