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-file-node-view-state.ts

@@ -0,0 +1,73 @@
+import { useRef } from 'react'
+
+export type FileNodeViewState = 'resolving' | 'ready' | 'missing'
+
+type ResolveFileNodeViewStateParams = {
+  hasFileTabId: boolean
+  hasCurrentFileNode: boolean
+  isNodeMapLoading: boolean
+  isNodeMapFetching: boolean
+  isNodeMapFetched: boolean
+  isNodeResolutionPending: boolean
+}
+
+type UseFileNodeViewStateParams = {
+  fileTabId: string | null
+  hasCurrentFileNode: boolean
+  isNodeMapLoading: boolean
+  isNodeMapFetching: boolean
+  isNodeMapFetched: boolean
+}
+
+export const resolveFileNodeViewState = ({
+  hasFileTabId,
+  hasCurrentFileNode,
+  isNodeMapLoading,
+  isNodeMapFetching,
+  isNodeMapFetched,
+  isNodeResolutionPending,
+}: ResolveFileNodeViewStateParams): FileNodeViewState => {
+  if (!hasFileTabId || hasCurrentFileNode)
+    return 'ready'
+
+  if (isNodeResolutionPending && (!isNodeMapFetched || isNodeMapLoading || isNodeMapFetching))
+    return 'resolving'
+
+  return 'missing'
+}
+
+export function useFileNodeViewState({
+  fileTabId,
+  hasCurrentFileNode,
+  isNodeMapLoading,
+  isNodeMapFetching,
+  isNodeMapFetched,
+}: UseFileNodeViewStateParams): FileNodeViewState {
+  const hasFileTabId = Boolean(fileTabId)
+  const resolutionRef = useRef<{ tabId: string | null, pending: boolean }>({
+    tabId: fileTabId,
+    pending: hasFileTabId,
+  })
+
+  if (resolutionRef.current.tabId !== fileTabId) {
+    resolutionRef.current = {
+      tabId: fileTabId,
+      pending: hasFileTabId,
+    }
+  }
+
+  if (fileTabId && resolutionRef.current.pending) {
+    const isQuerySettled = isNodeMapFetched && !isNodeMapLoading && !isNodeMapFetching
+    if (hasCurrentFileNode || isQuerySettled)
+      resolutionRef.current.pending = false
+  }
+
+  return resolveFileNodeViewState({
+    hasFileTabId,
+    hasCurrentFileNode,
+    isNodeMapLoading,
+    isNodeMapFetching,
+    isNodeMapFetched,
+    isNodeResolutionPending: resolutionRef.current.pending,
+  })
+}