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

src/styles/globals.css

@@ -240,4 +240,12 @@
   [data-slot="tabs-trigger"][data-state="active"] {
     @apply bg-background text-foreground shadow;
   }
-}
+}
+
+/* Viewport height constraint for proper flex layout */
+html,
+body,
+#__next {
+  height: 100%;
+  min-height: 100vh;
+}