feat: update backend OCR parser, web app, mobile app camera/preview UI, tests, and documentation with sample images

lib/features/auth/auth_provider.dart

@@ -28,7 +28,15 @@ class AuthNotifier extends StateNotifier<bool> {
         },
       );
       
+      if (response.data is! Map || response.data['data'] is! Map) {
+        throw Exception("Format respon server tidak valid (bukan JSON)");
+      }
+      
       final token = response.data['data']['token'];
+      if (token == null) {
+        throw Exception("Token otentikasi tidak ditemukan dalam respon");
+      }
+      
       final prefs = await SharedPreferences.getInstance();
       await prefs.setString('auth_token', token);