Adds empty-server auto-stop to the reconciler. When Idle.AutoStopEnabled
is true and the RCON player tally is zero for EmptySecondsBeforeStop seconds,
the operator flips desiredState to Stopped, which triggers the normal
graceful-shutdown path.
- Add EmptySince status field to track empty duration
- Clear EmptySince on stop and when players return
- Reuse existing RCON probe's player count (zero extra network cost)
- 4 new test cases covering timestamp, timeout, player-join reset, and
disabled-by-default