feat: Implement entity join functionality in V2Repeater and configuration panel

- Added support for entity joins in the V2Repeater component, allowing for automatic resolution of foreign key references to display data from related tables.
- Introduced a new `resolveEntityJoins` function to handle the fetching and mapping of reference data based on configured entity joins.
- Enhanced the V2RepeaterConfigPanel to manage entity join configurations, including loading available columns and toggling join settings.
- Updated the data handling logic to incorporate mapping rules for incoming data, ensuring that only necessary fields are retained during processing.
- Improved user experience by providing clear logging and feedback during entity join resolution and data mapping operations.

frontend/lib/registry/components/universal-form-modal/UniversalFormModalComponent.tsx

@@ -468,6 +468,11 @@ export function UniversalFormModalComponent({
         console.log(`[UniversalFormModal] 원본 그룹 데이터 병합: ${originalGroupedData.length}개`);
       }
 
+      // 분할패널에서 전달한 메인 레코드 ID 전달
+      if (latestFormData._mainRecordId) {
+        event.detail.formData._mainRecordId = latestFormData._mainRecordId;
+      }
+
       // 🆕 부모 formData의 중첩 객체(modalKey)도 최신 데이터로 업데이트
       // onChange(setTimeout)가 아직 부모에 전파되지 않았을 수 있으므로 직접 업데이트
       for (const parentKey of Object.keys(event.detail.formData)) {
@@ -993,6 +998,11 @@ export function UniversalFormModalComponent({
       }
     }
 
+    // 분할패널에서 전달한 메인 레코드 ID 보존
+    if (effectiveInitialData?._mainRecordId) {
+      newFormData._mainRecordId = effectiveInitialData._mainRecordId;
+    }
+
     setFormData(newFormData);
     formDataRef.current = newFormData;
     setRepeatSections(newRepeatSections);