feat: Enhance V2Repeater and configuration panel with source detail auto-fetching

- Added support for automatic fetching of detail rows from the master data in the V2Repeater component, improving data management.
- Introduced a new configuration option in the V2RepeaterConfigPanel to enable source detail auto-fetching, allowing users to specify detail table and foreign key settings.
- Enhanced the V2Repeater component to handle entity joins for loading data, optimizing data retrieval processes.
- Updated the V2RepeaterProps and V2RepeaterConfig interfaces to include new properties for grouped data and source detail configuration, ensuring type safety and clarity in component usage.
- Improved logging for data loading processes to provide better insights during development and debugging.

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

@@ -47,14 +47,22 @@ export function UniversalFormModalConfigPanel({
   onChange,
   allComponents = [],
 }: UniversalFormModalConfigPanelProps) {
-  // config가 불완전할 수 있으므로 defaultConfig와 병합하여 안전하게 사용
+  // V2 레이아웃에서 overrides 전체가 componentConfig로 전달되는 경우
+  // 실제 설정이 rawConfig.componentConfig에 이중 중첩되어 있을 수 있음
+  // 평탄화된 구조(save 후)가 있으면 우선, 아니면 중첩 구조에서 추출
+  const nestedConfig = rawConfig?.componentConfig;
+  const hasFlatConfig = rawConfig?.modal !== undefined || rawConfig?.sections !== undefined;
+  const effectiveConfig = hasFlatConfig
+    ? rawConfig
+    : (nestedConfig?.modal ? nestedConfig : rawConfig);
+
   const config: UniversalFormModalConfig = {
     ...defaultConfig,
-    ...rawConfig,
-    modal: { ...defaultConfig.modal, ...rawConfig?.modal },
-    sections: rawConfig?.sections ?? defaultConfig.sections,
-    saveConfig: { ...defaultConfig.saveConfig, ...rawConfig?.saveConfig },
-    editMode: { ...defaultConfig.editMode, ...rawConfig?.editMode },
+    ...effectiveConfig,
+    modal: { ...defaultConfig.modal, ...effectiveConfig?.modal },
+    sections: effectiveConfig?.sections ?? defaultConfig.sections,
+    saveConfig: { ...defaultConfig.saveConfig, ...effectiveConfig?.saveConfig },
+    editMode: { ...defaultConfig.editMode, ...effectiveConfig?.editMode },
   };
 
   // 테이블 목록