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/Cargo.toml

@@ -0,0 +1,18 @@
+[package]
+name = "holzleitner-domain"
+version.workspace = true
+edition.workspace = true
+license.workspace = true
+authors.workspace = true
+
+[features]
+# Opt-in: schaltet `utoipa::ToSchema`-Ableitungen für die OpenAPI-
+# Generierung in der API-Schicht frei. Konsumenten ohne OpenAPI-Bedarf
+# (z. B. CLI-Tools, Tests) bleiben utoipa-frei.
+openapi = ["dep:utoipa"]
+
+[dependencies]
+serde.workspace = true
+uuid.workspace = true
+chrono.workspace = true
+utoipa = { workspace = true, optional = true }