Reset the FT0 photon track ids at the end of each event

This fixes hits that depended on the previous event of the same worker.

- mTrackIdTop and mTrackIdMCPtop kept their values across events.
- A photon in the next event with the same track id then skipped the photo-electron registration.
- Both are now reset in Reset().

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: sawenzel

Detectors/FIT/FT0/simulation/src/Detector.cxx

@@ -1218,6 +1218,8 @@ void Detector::Reset()
     mHits->clear();
   }
   mTrackRefLastTrackID = -1;
+  mTrackIdTop = -1;
+  mTrackIdMCPtop = -1;
 }
 
 void Detector::CreateMaterials()