feat: Redesign the designer layout using a grid system, adding explicit left, center, and right panels with collapse functionality.

src/app/(dashboard)/studies/[id]/experiments/[experimentId]/designer/DesignerPageClient.tsx

@@ -55,9 +55,5 @@ export function DesignerPageClient({
     },
   ]);
 
-  return (
-    <div className="h-[calc(100vh-4rem-2rem)] w-full overflow-hidden border rounded-lg bg-background">
-      <DesignerRoot experimentId={experiment.id} initialDesign={initialDesign} />
-    </div>
-  );
+  return <DesignerRoot experimentId={experiment.id} initialDesign={initialDesign} />;
 }