fix: ViewTransitionOutlet needs h-full for React Flow canvas

The wrapper div broke the height chain needed by TreeEditorPage's
h-full layout, causing React Flow canvas to collapse to zero height.

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

frontend/src/components/layout/ViewTransitionOutlet.tsx

@@ -14,7 +14,7 @@ export function ViewTransitionOutlet() {
   const routeKey = segments.slice(0, 2).join('/') || '/'
 
   return (
-    <div key={routeKey} className="animate-fade-in-up">
+    <div key={routeKey} className="h-full animate-fade-in-up">
       <Outlet />
     </div>
   )