fix: add delete/bookmark actions for blueprints in V2 node library sidebar (#10827)

## Summary

Add missing delete and bookmark actions for user blueprints in the V2
node library sidebar, fixing parity with the V1 sidebar.

## Changes

- **What**: 
- Add delete button (inline + context menu) for user blueprints in
`TreeExplorerV2Node` and `TreeExplorerV2`
- Extract `isUserBlueprint()` helper in `subgraphStore` for DRY usage
across V1/V2 sidebars


![Kapture 2026-04-03 at 00 12
09](https://github.com/user-attachments/assets/3f1f3f41-ed2b-4250-953f-511d39e54e45)

## Review Focus

- `isUserBlueprint` consolidates logic previously duplicated between
`NodeTreeLeaf` and the new V2 components
- Context menu guard `contextMenuNode?.data` prevents showing empty
menus
- Folder `@contextmenu` handler clears stale `contextMenuNode` to
prevent wrong actions

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-10827-fix-add-delete-bookmark-actions-for-blueprints-in-V2-node-library-sidebar-3366d73d36508111afd2c2c7d8ff0220)
by [Unito](https://www.unito.io)

src/components/sidebar/tabs/nodeLibrary/AllNodesPanel.vue

@@ -12,7 +12,6 @@
       :root="favoritesRoot"
       show-context-menu
       @node-click="(node) => emit('nodeClick', node)"
-      @add-to-favorites="handleAddToFavorites"
     />
     <div v-else class="px-6 py-2 text-xs text-muted-background">
       {{ $t('sideToolbar.nodeLibraryTab.noBookmarkedNodes') }}
@@ -31,7 +30,6 @@
         :root="section.root"
         show-context-menu
         @node-click="(node) => emit('nodeClick', node)"
-        @add-to-favorites="handleAddToFavorites"
       />
     </div>
   </div>
@@ -71,12 +69,4 @@ const hasFavorites = computed(
 const favoritesRoot = computed(() =>
   fillNodeInfo(nodeBookmarkStore.bookmarkedRoot)
 )
-
-function handleAddToFavorites(
-  node: RenderedTreeExplorerNode<ComfyNodeDefImpl>
-) {
-  if (node.data) {
-    nodeBookmarkStore.toggleBookmark(node.data)
-  }
-}
 </script>