Updates documents backend service and API to support multi-vehicle insurance documents:
- Service: createDocument/updateDocument validate and handle sharedVehicleIds for insurance docs
- Service: addVehicleToDocument validates ownership and adds vehicles to shared array
- Service: removeVehicleFromDocument with context-aware delete logic:
- Shared vehicle only: remove from array
- Primary with no shared: soft delete document
- Primary with shared: promote first shared to primary
- Service: getDocumentsByVehicle returns all docs for a vehicle (primary or shared)
- Controller: Added handlers for listByVehicle, addVehicle, removeVehicle with proper error handling
- Routes: Added POST/DELETE /documents/:id/vehicles/:vehicleId and GET /documents/by-vehicle/:vehicleId
- Validation: Added DocumentVehicleParamsSchema for vehicle management routes
Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
