fix: enable scrolling in node editor panel sidebar

Add min-h-0 to flex containers in the ancestor chain so overflow-y-auto
actually triggers instead of content overflowing off-screen.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/components/tree-editor/TreeEditorLayout.tsx

@@ -33,7 +33,7 @@ export function TreeEditorLayout({
   return (
     <div
       className={cn(
-        'flex flex-1 overflow-hidden',
+        'flex min-h-0 flex-1 overflow-hidden',
         isMobile ? 'flex-col' : 'flex-row'
       )}
     >