Resolve VSN-2113 "Feature/add date-based trip preview with absence filtering"
- Add history tracking for circuit schedule changes with initial snapshot saved after first trip generation.
- New endpoint supports two modes: MODIFY_EXISTING: apply schedule changes immediately to current trips CREATE_NEW: store changes for a future period with start/end dates
- Scheduled job at midnight applies pending changes when startDate arrives and reverts to the previous valid schedule when a period expires. Closes VSN-2113