Phase A: generierter Dart-Client + DI-Foundation für Rust-Backend

OpenAPI-Generator-Setup:
- tool/generate_api_client.sh: Direkter Aufruf der openapi-generator-cli.jar
  (Java-CLI statt Dart-build_runner-Integration — vermeidet die
  analyzer-/source_gen-Version-Hölle mit json_serializable)
- tool/fetch_openapi_generator.sh: lädt die JAR (29 MB) nach (gitignored)
- openapi/holzleitner.json: Snapshot der Backend-Spec für reproduzierbare
  Generation
- packages/holzleitner_api/: generiertes Dart-Sub-Package (built_value +
  dio), per path-dep im Haupt-pubspec eingehängt

Netzwerk-Layer (lib/data/network/):
- BackendConfig: API- und Keycloak-Endpoints für Local-Dev (localhost
  wegen Keycloak-iss-Claim).
- AuthTokenProvider-Schnittstelle.
- DevPasswordGrantTokenProvider: Phase-A-Provider via Keycloak
  password-grant, Token-Caching mit Expiry-Check (Phase B ersetzt das
  durch flutter_appauth PKCE).
- HolzleitnerAuthInterceptor: dynamischer Bearer-Inject pro Request.
- HolzleitnerApiFactory: baut die generierte HolzleitnerApi-Klasse
  mit unserem Interceptor statt der vier Default-Auth-Interceptors.
- network_locator.registerNetworking(): get_it-Setup, in main() vor
  runApp() aufgerufen.

Clean-Arch-Scaffolding (lib/data/, lib/domain/):
- Verzeichnisstruktur für Phase C+D angelegt (mapper/, repository/,
  entity/, repository/) — befüllt sich in den Folge-Phasen.

Smoke-Test:
- tool/smoke_test_api.dart ruft /health (ungeschützt) und /me/cars
  (mit Bearer) via generiertem Client — grün gegen lokales Backend.

packages/holzleitner_api/lib/src/model/car_response.dart

@@ -0,0 +1,107 @@
+//
+// AUTO-GENERATED FILE, DO NOT MODIFY!
+//
+
+// ignore_for_file: unused_element
+import 'package:holzleitner_api/src/model/car.dart';
+import 'package:built_value/built_value.dart';
+import 'package:built_value/serializer.dart';
+
+part 'car_response.g.dart';
+
+/// CarResponse
+///
+/// Properties:
+/// * [car] 
+@BuiltValue()
+abstract class CarResponse implements Built<CarResponse, CarResponseBuilder> {
+  @BuiltValueField(wireName: r'car')
+  Car get car;
+
+  CarResponse._();
+
+  factory CarResponse([void updates(CarResponseBuilder b)]) = _$CarResponse;
+
+  @BuiltValueHook(initializeBuilder: true)
+  static void _defaults(CarResponseBuilder b) => b;
+
+  @BuiltValueSerializer(custom: true)
+  static Serializer<CarResponse> get serializer => _$CarResponseSerializer();
+}
+
+class _$CarResponseSerializer implements PrimitiveSerializer<CarResponse> {
+  @override
+  final Iterable<Type> types = const [CarResponse, _$CarResponse];
+
+  @override
+  final String wireName = r'CarResponse';
+
+  Iterable<Object?> _serializeProperties(
+    Serializers serializers,
+    CarResponse object, {
+    FullType specifiedType = FullType.unspecified,
+  }) sync* {
+    yield r'car';
+    yield serializers.serialize(
+      object.car,
+      specifiedType: const FullType(Car),
+    );
+  }
+
+  @override
+  Object serialize(
+    Serializers serializers,
+    CarResponse object, {
+    FullType specifiedType = FullType.unspecified,
+  }) {
+    return _serializeProperties(serializers, object, specifiedType: specifiedType).toList();
+  }
+
+  void _deserializeProperties(
+    Serializers serializers,
+    Object serialized, {
+    FullType specifiedType = FullType.unspecified,
+    required List<Object?> serializedList,
+    required CarResponseBuilder result,
+    required List<Object?> unhandled,
+  }) {
+    for (var i = 0; i < serializedList.length; i += 2) {
+      final key = serializedList[i] as String;
+      final value = serializedList[i + 1];
+      switch (key) {
+        case r'car':
+          final valueDes = serializers.deserialize(
+            value,
+            specifiedType: const FullType(Car),
+          ) as Car;
+          result.car.replace(valueDes);
+          break;
+        default:
+          unhandled.add(key);
+          unhandled.add(value);
+          break;
+      }
+    }
+  }
+
+  @override
+  CarResponse deserialize(
+    Serializers serializers,
+    Object serialized, {
+    FullType specifiedType = FullType.unspecified,
+  }) {
+    final result = CarResponseBuilder();
+    final serializedList = (serialized as Iterable<Object?>).toList();
+    final unhandled = <Object?>[];
+    _deserializeProperties(
+      serializers,
+      serialized,
+      specifiedType: specifiedType,
+      serializedList: serializedList,
+      unhandled: unhandled,
+      result: result,
+    );
+    return result.build();
+  }
+}
+