Initial: Rust-Backend mit Clean Architecture (domain/application/infrastructure/api)

Vier-Crate-Workspace mit:
- Domain: Account, Car, Tour, Delivery, DeliveryItem, DeliveryNote, Customer,
  Article, Warehouse, ScanState, AuditAction — alle mit serde + feature-gated
  utoipa::ToSchema.
- Application: Ports (TourRepository, DeliveryRepository, ScanRepository,
  DeliveryNoteRepository, CarRepository, AuthService) und Use Cases.
- Infrastructure: Postgres-Adapter via sqlx (PgTourRepository etc.) +
  Keycloak-AuthService mit JWKS-Cache + OIDC-Discovery.
- API: Axum 0.8, utoipa-OpenAPI + Swagger-UI, JWT-Bearer-Middleware,
  AuthenticatedUser-Extractor.

Endpoints:
- GET /me/tours/today, /tours/{id}, /accounts/{pn}, /me/cars, /health
- POST /sync/tour, /scans (bulk + idempotent via clientScanId),
  /deliveries/{id}/{hold,resume,cancel,complete,notes}, /me/cars
- PUT /tours/{id}/delivery-order, /deliveries/{id}/assigned-car, /me/cars/{id}
- PATCH /me/cars/{id}

Datenmodell:
- 6 Migrationen (accounts, tours/deliveries/items + Stammdaten,
  scan_audit mit clientScanId-UNIQUE, state_reason refactor,
  delivery_notes, cars + FKs nachziehen).
- Business-stabile Beleg-Keys (belegart_id, belegnummer) für ERP-Sync.
- Append-only scan_audit + embedded scan_state als doppelte Wahrheit.

Dev-Setup:
- docker-compose mit Postgres 17 + Keycloak 26
- Keycloak-Realm 'holzleitner' mit Public-Client (PKCE), Testfahrer
  (PN 1001) + Audience-/Personalnummer-Mapper

crates/application/src/usecases/set_delivery_order.rs

@@ -0,0 +1,53 @@
+use std::collections::HashSet;
+use std::sync::Arc;
+
+use uuid::Uuid;
+
+use crate::dto::{SetDeliveryOrderRequest, SetDeliveryOrderResponse};
+use crate::error::ApplicationError;
+use crate::ports::TourRepository;
+
+/// Schreibt die Sortier-Reihenfolge aller Lieferungen einer Tour neu.
+///
+/// Eingabe-Validierung (vor DB-Aufruf):
+/// * mindestens eine Id
+/// * keine Duplikate
+///
+/// Die Mengen-Übereinstimmung mit der Tour wird in der Persistence
+/// geprüft (braucht DB-Kontext).
+pub struct SetDeliveryOrderUseCase {
+    repository: Arc<dyn TourRepository>,
+}
+
+impl SetDeliveryOrderUseCase {
+    pub fn new(repository: Arc<dyn TourRepository>) -> Self {
+        Self { repository }
+    }
+
+    pub async fn execute(
+        &self,
+        tour_id: Uuid,
+        request: SetDeliveryOrderRequest,
+    ) -> Result<SetDeliveryOrderResponse, ApplicationError> {
+        if request.delivery_ids.is_empty() {
+            return Err(ApplicationError::Validation(
+                "delivery_ids darf nicht leer sein".into(),
+            ));
+        }
+        let mut seen = HashSet::with_capacity(request.delivery_ids.len());
+        for id in &request.delivery_ids {
+            if !seen.insert(*id) {
+                return Err(ApplicationError::Validation(format!(
+                    "delivery_id {id} kommt mehrfach vor"
+                )));
+            }
+        }
+
+        let order = self
+            .repository
+            .set_delivery_order(tour_id, &request.delivery_ids)
+            .await?;
+
+        Ok(SetDeliveryOrderResponse { tour_id, order })
+    }
+}