test: 통합 테스트 오류 및 경고 수정

- 모든 서비스 메서드 시그니처를 실제 구현에 맞게 수정
- TestDataGenerator 제거하고 직접 객체 생성으로 변경
- 모델 필드명 및 타입 불일치 수정
- 불필요한 Either 패턴 사용 제거
- null safety 관련 이슈 해결

수정된 파일:
- test/integration/screens/company_integration_test.dart
- test/integration/screens/equipment_integration_test.dart
- test/integration/screens/user_integration_test.dart
- test/integration/screens/login_integration_test.dart

lib/screens/overview/overview_screen_redesign.dart

@@ -466,7 +466,7 @@ class _OverviewScreenRedesignState extends State<OverviewScreenRedesign> {
       }
     }
 
-    final color = getActivityColor(activity.type);
+    final color = getActivityColor(activity.activityType);
     final dateFormat = DateFormat('MM/dd HH:mm');
 
     return Padding(
@@ -480,7 +480,7 @@ class _OverviewScreenRedesignState extends State<OverviewScreenRedesign> {
               borderRadius: BorderRadius.circular(6),
             ),
             child: Icon(
-              getActivityIcon(activity.type),
+              getActivityIcon(activity.activityType),
               color: color,
               size: 16,
             ),
@@ -491,7 +491,7 @@ class _OverviewScreenRedesignState extends State<OverviewScreenRedesign> {
               crossAxisAlignment: CrossAxisAlignment.start,
               children: [
                 Text(
-                  activity.title,
+                  activity.entityName,
                   style: ShadcnTheme.bodyMedium,
                 ),
                 Text(
@@ -502,7 +502,7 @@ class _OverviewScreenRedesignState extends State<OverviewScreenRedesign> {
             ),
           ),
           Text(
-            dateFormat.format(activity.createdAt),
+            dateFormat.format(activity.timestamp),
             style: ShadcnTheme.bodySmall,
           ),
         ],