feat: Apply entity navigation arrows to 27 additional sections (VSN-2238)
Add prev/next navigation (EntityNavigationArrows + useEntityNavigation) to:
- Absence usager, Avenant, Circuit, Client, Contract
- Establishment (attendance + form), Class-level
- Infrastructure: Agency, Department, Lot, Sector
- Trajet, Usager
Also apply null-ID guard (.filter(x => x.id != null)) on all ID arrays to prevent 'null'/'undefined' string entries in navigation.
Closes VSN-2238