Resolve VSN-2327 "Refactor/optimize circuit mass import, fix date parsing, and add safety rollbacks"

• Group passengers by circuit code to process assignments in batches, significantly reducing database calls.
• Trigger `PreparedTrip` generation automatically immediately after a successful passenger assignment during the import.
• Implement manual rollback mechanism: automatically delete newly created `PreparedCircuit` records if passenger assignment fails (e.g., due to out-of-bounds dates) to prevent empty ghost circuits.
• Enforce `dd/mm/yyyy` cell style for date columns in the dynamic passenger template generation to ensure consistent user input.

Closes VSN-2327