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/domain/src/tour.rs

@@ -0,0 +1,20 @@
+use chrono::{DateTime, NaiveDate, Utc};
+use serde::{Deserialize, Serialize};
+use uuid::Uuid;
+
+/// Tour eines Tages, pro [`crate::domain::Account`]. Aggregat-Wurzel
+/// für die Lieferungen dieses Tages — die einzelnen [`crate::domain::Delivery`]
+/// referenzieren ihre Tour per FK.
+///
+/// Der Sync vom ERP läuft in der Regel einmal am Vortag und füllt eine
+/// neue Tour-Zeile inklusive Delivery- und DeliveryItem-Strukturen.
+#[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq)]
+#[cfg_attr(feature = "openapi", derive(utoipa::ToSchema))]
+#[serde(rename_all = "camelCase")]
+pub struct Tour {
+    pub id: Uuid,
+    pub account_id: i64,
+    pub date: NaiveDate,
+    /// Zeitpunkt des letzten ERP-Sync — für Drift-Erkennung.
+    pub synced_at: DateTime<Utc>,
+}