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/create_delivery_note.rs

@@ -0,0 +1,73 @@
+use std::sync::Arc;
+
+use uuid::Uuid;
+
+use holzleitner_domain::DeliveryNote;
+
+use crate::dto::CreateDeliveryNoteRequest;
+use crate::error::ApplicationError;
+use crate::ports::{CarRepository, DeliveryNoteRepository};
+
+/// Legt eine neue Notiz an einer Lieferung an.
+///
+/// Validierung:
+/// * mindestens eines von `text` (nicht-leer nach trim) und
+///   `image_attachment` (nicht-leer nach trim) muss gesetzt sein.
+/// * `author_car_id` muss — falls gesetzt — zum angemeldeten Account gehören.
+pub struct CreateDeliveryNoteUseCase {
+    repository: Arc<dyn DeliveryNoteRepository>,
+    cars: Arc<dyn CarRepository>,
+}
+
+impl CreateDeliveryNoteUseCase {
+    pub fn new(
+        repository: Arc<dyn DeliveryNoteRepository>,
+        cars: Arc<dyn CarRepository>,
+    ) -> Self {
+        Self { repository, cars }
+    }
+
+    pub async fn execute(
+        &self,
+        delivery_id: Uuid,
+        author_personalnummer: i64,
+        request: CreateDeliveryNoteRequest,
+    ) -> Result<DeliveryNote, ApplicationError> {
+        let text = clean(request.text);
+        let image = clean(request.image_attachment);
+
+        if text.is_none() && image.is_none() {
+            return Err(ApplicationError::Validation(
+                "notiz braucht text oder image_attachment".into(),
+            ));
+        }
+
+        if let Some(car_id) = request.author_car_id {
+            self.cars
+                .assert_owned_by_account(&[car_id], author_personalnummer)
+                .await?;
+        }
+
+        self.repository
+            .create(
+                delivery_id,
+                author_personalnummer,
+                request.author_car_id,
+                text,
+                image,
+            )
+            .await
+    }
+}
+
+/// Trim + leerer-String → None.
+fn clean(input: Option<String>) -> Option<String> {
+    input.and_then(|s| {
+        let trimmed = s.trim();
+        if trimmed.is_empty() {
+            None
+        } else {
+            Some(trimmed.to_owned())
+        }
+    })
+}