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)

packages/design-system/src/css/style.css

@@ -16,7 +16,7 @@
 @plugin "./lucideStrokePlugin.js";
 
 /* Safelist dynamic comfy icons for node library folders */
-@source inline("icon-[comfy--{ai-model,bfl,bria,bytedance,credits,elevenlabs,extensions-blocks,file-output,gemini,grok,hitpaw,ideogram,image-ai-edit,kling,ltxv,luma,magnific,mask,meshy,minimax,moonvalley-marey,node,openai,pin,pixverse,play,recraft,reve,rodin,runway,sora,stability-ai,template,tencent,topaz,tripo,veo,vidu,wan,wavespeed,workflow,quiver-ai}]");
+@source inline("icon-[comfy--{ai-model,bfl,bria,bytedance,credits,elevenlabs,extensions-blocks,file-output,gemini,grok,hitpaw,ideogram,image-ai-edit,kling,ltxv,luma,magnific,mask,meshy,minimax,moonvalley-marey,node,openai,pin,pixverse,play,recraft,reve,rodin,runway,sora,stability-ai,template,tencent,topaz,tripo,veo,vidu,wan,wavespeed,workflow,quiver}]");
 
 /* Safelist dynamic comfy icons for essential nodes (kebab-case of node names) */
 @source inline("icon-[comfy--{save-image,load-video,save-video,load-3-d,save-glb,image-batch,batch-images-node,image-crop,image-scale,image-rotate,image-blur,image-invert,canny,recraft-remove-background-node,kling-lip-sync-audio-to-video-node,load-audio,save-audio,stability-text-to-audio,lora-loader,lora-loader-model-only,primitive-string-multiline,get-video-components,video-slice,tencent-text-to-model-node,tencent-image-to-model-node,open-ai-chat-node,preview-image,image-and-mask-preview,layer-mask-mask-preview,mask-preview,image-preview-from-latent,i-tools-preview-image,i-tools-compare-image,canny-to-image,image-edit,text-to-image,pose-to-image,depth-to-video,image-to-image,canny-to-video,depth-to-image,image-to-video,pose-to-video,text-to-video,image-inpainting,image-outpainting}]");