Move library collections as a group and map v2 identity refs.

Collapsed collection actions now move, rename, delete, and rerun every part so chains stay together. Identity mode follows the v2u3 Ref2VA picture wiring.

Co-authored-by: Cursor <cursoragent@cursor.com>

server/api/library/stills.post.ts

@@ -33,5 +33,5 @@ export default defineEventHandler(async (event) => {
     height: Number(fields.height || 0),
     hideInput: fields.hideInput === 'true'
   })
-  return { still, ...publicLibrary(event) }
+  return { still: still || undefined, ...publicLibrary(event) }
 })