VSN-2942/feat(exploitation): readable « N° » code SEC/AGE/DEP/LOT/ETA/CON with sort and filter

Replace the UUID in the « N° » column with a contiguous sequential code (sequentialNumber + sequentialCode) on the sector, agency, department, lot, establishment and contract DTOs, allocated on creation and on import via the shared EntitySequenceService counter. Add sort and filter by sequence number (SEC1 / sec1 / 1) for all six infrastructure entities via FilterSpecUtils.sequentialNumberPredicate and id → sequentialNumber sorting.