Flutter-Tests: ApiClient, Offline-Queue, Login-/Objektliste-Widgets

ApiClient nimmt jetzt einen injizierbaren http.Client entgegen (Testbarkeit,
kein Verhaltensunterschied im Betrieb). Tests mocken ihn mit mocktail statt
echter Netzwerkaufrufe. offline_queue_test.dart nutzt sqflite_common_ffi
(reines Dart) für die Queue-Logik ohne Gerät/Emulator: Erfolg entfernt
Eintrag, Netzwerkfehler bleibt "wartet", 4xx setzt "fehler" ohne Auto-Retry.
Dazu Widget-Tests für Login-Flow und Objektliste-Suchfilter.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CVgbozhYmuEhiEJHffRXCV

flutter_app/lib/api/api_client.dart

@@ -17,9 +17,10 @@ class ApiException implements Exception {
 }
 
 class ApiClient {
-  ApiClient({required this.baseUrl});
+  ApiClient({required this.baseUrl, http.Client? httpClient}) : _http = httpClient ?? http.Client();
 
   final String baseUrl;
+  final http.Client _http;
   String? _token;
 
   Future<void> ladeToken() async {
@@ -40,7 +41,7 @@ class ApiClient {
   bool get istEingeloggt => _token != null;
 
   Future<String> login(String username, String password) async {
-    final response = await http.post(
+    final response = await _http.post(
       Uri.parse('$baseUrl/auth/login'),
       headers: {'Content-Type': 'application/x-www-form-urlencoded'},
       body: {'username': username, 'password': password},
@@ -69,19 +70,19 @@ class ApiClient {
     late http.Response response;
     switch (method) {
       case 'POST':
-        response = await http.post(uri, headers: headers, body: encodedBody);
+        response = await _http.post(uri, headers: headers, body: encodedBody);
         break;
       case 'PUT':
-        response = await http.put(uri, headers: headers, body: encodedBody);
+        response = await _http.put(uri, headers: headers, body: encodedBody);
         break;
       case 'PATCH':
-        response = await http.patch(uri, headers: headers, body: encodedBody);
+        response = await _http.patch(uri, headers: headers, body: encodedBody);
         break;
       case 'DELETE':
-        response = await http.delete(uri, headers: headers);
+        response = await _http.delete(uri, headers: headers);
         break;
       default:
-        response = await http.get(uri, headers: headers);
+        response = await _http.get(uri, headers: headers);
     }
 
     if (response.statusCode >= 400) {