refactored data providers with centralized cache resolution, unified UI using custom dialogs and bottom sheets, and enhanced network error handling for Dio and TLS errors

test/api/errors/error_mapper_test.dart

@@ -1,6 +1,7 @@
 import 'dart:async';
 import 'dart:io';
 
+import 'package:dio/dio.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:http/http.dart' as http;
 import 'package:marianum_mobile/api/api_error.dart';
@@ -36,8 +37,9 @@ void main() {
     });
 
     test('HandshakeException maps to a TLS-specific message', () {
-      expect(errorToUserMessage(const HandshakeException('bad cert')),
-          'Sichere Verbindung konnte nicht hergestellt werden.');
+      final message = errorToUserMessage(const HandshakeException('bad cert'));
+      expect(message, contains('sichere Verbindung'));
+      expect(message, contains('Geräte-Uhrzeit'));
     });
 
     test('FormatException maps to ParseException message', () {
@@ -63,6 +65,34 @@ void main() {
     test('custom fallback overrides the default', () {
       expect(errorToUserMessage(null, fallback: 'meins'), 'meins');
     });
+
+    test('DioException connectionTimeout maps to timeout NetworkException', () {
+      final ex = DioException(
+        requestOptions: RequestOptions(path: '/x'),
+        type: DioExceptionType.connectionTimeout,
+      );
+      expect(errorToUserMessage(ex), NetworkException.timeout().userMessage);
+    });
+
+    test('DioException connectionError maps to NetworkException', () {
+      final ex = DioException(
+        requestOptions: RequestOptions(path: '/x'),
+        type: DioExceptionType.connectionError,
+      );
+      expect(errorToUserMessage(ex), const NetworkException().userMessage);
+    });
+
+    test('DioException badResponse maps to a server status message', () {
+      final ex = DioException(
+        requestOptions: RequestOptions(path: '/x'),
+        type: DioExceptionType.badResponse,
+        response: Response(
+          requestOptions: RequestOptions(path: '/x'),
+          statusCode: 503,
+        ),
+      );
+      expect(errorToUserMessage(ex), contains('503'));
+    });
   });
 
   group('errorToTechnicalDetails', () {