refactor(skill)!: add file node view-state flow and mode-based file data hook

- introduce resolving/ready/missing node view-state to avoid unsupported flicker

- switch useSkillFileData to explicit mode: none/content/download

- add hook tests for view-state transitions and mode query gating

BREAKING CHANGE: useSkillFileData signature changed from (appId, nodeId, isEditable) to (appId, nodeId, mode).

web/app/components/workflow/skill/hooks/use-skill-file-data.ts

@@ -1,5 +1,7 @@
 import { useGetAppAssetFileContent, useGetAppAssetFileDownloadUrl } from '@/service/use-app-asset'
 
+export type SkillFileDataMode = 'none' | 'content' | 'download'
+
 export type SkillFileDataResult = {
   fileContent: ReturnType<typeof useGetAppAssetFileContent>['data']
   downloadUrlData: ReturnType<typeof useGetAppAssetFileDownloadUrl>['data']
@@ -9,19 +11,22 @@ export type SkillFileDataResult = {
 
 /**
  * Hook to fetch file data for skill documents.
- * Fetches content for editable files and download URL for non-editable files.
+ * Uses explicit mode to control data fetching:
+ * - 'content': fetch editable file content
+ * - 'download': fetch non-editable file download URL
+ * - 'none': skip file-related requests while node metadata is unresolved
  */
 export function useSkillFileData(
   appId: string,
   nodeId: string | null | undefined,
-  isEditable: boolean,
+  mode: SkillFileDataMode,
 ): SkillFileDataResult {
   const {
     data: fileContent,
     isLoading: isContentLoading,
     error: contentError,
   } = useGetAppAssetFileContent(appId, nodeId || '', {
-    enabled: isEditable,
+    enabled: mode === 'content',
   })
 
   const {
@@ -29,11 +34,19 @@ export function useSkillFileData(
     isLoading: isDownloadUrlLoading,
     error: downloadUrlError,
   } = useGetAppAssetFileDownloadUrl(appId, nodeId || '', {
-    enabled: !isEditable && !!nodeId,
+    enabled: mode === 'download' && !!nodeId,
   })
 
-  const isLoading = isEditable ? isContentLoading : isDownloadUrlLoading
-  const error = isEditable ? contentError : downloadUrlError
+  const isLoading = mode === 'content'
+    ? isContentLoading
+    : mode === 'download'
+      ? isDownloadUrlLoading
+      : false
+  const error = mode === 'content'
+    ? contentError
+    : mode === 'download'
+      ? downloadUrlError
+      : null
 
   return {
     fileContent,