Extract resticEnv/sendStarted/streamHandler/sendFinished helpers to remove
boilerplate duplication across Run* methods. Add RunPrune (ships repo.stats
with LastPruneAt before job.finished), RunCheck (ships stats with
LastCheckStatus/LockPresent regardless of outcome), RunUnlock (ships
LockPresent=false on success), and reportStats (fills size fields via
RunStats when caller didn't populate them).
Wire JobPrune/JobCheck/JobUnlock into the dispatcher switch; teach
MsgConfigUpdate about the Slot discriminator for admin vs repo creds;
add strconv import for subset-pct parsing.
