feat: deep-link sidebar Layouts to specific design surface

- Sidebar Layouts items now link to /design?surface=<surfaceId>
- Design page reads ?surface= param and opens that surface directly
- DesignPage split into DesignPageInner + Suspense wrapper so
  useSearchParams works in the Next.js static build

Made-with: Cursor

app/[workspace]/project/[projectId]/design/page.tsx

@@ -1,6 +1,7 @@
 "use client";
 
-import { use, useState, useEffect } from "react";
+import { use, useState, useEffect, Suspense } from "react";
+import { useSearchParams } from "next/navigation";
 import { toast } from "sonner";
 import {
   SCAFFOLD_REGISTRY, THEME_REGISTRY,
@@ -958,8 +959,9 @@ function SurfacePicker({
 // Page
 // ---------------------------------------------------------------------------
 
-export default function DesignPage({ params }: { params: Promise<{ workspace: string; projectId: string }> }) {
-  const { projectId } = use(params);
+function DesignPageInner({ projectId }: { projectId: string }) {
+  const searchParams = useSearchParams();
+  const requestedSurface = searchParams.get("surface");
 
   const [surfaces, setSurfaces] = useState<string[]>([]);
   const [surfaceThemes, setSurfaceThemes] = useState<Record<string, string>>({});
@@ -979,7 +981,11 @@ export default function DesignPage({ params }: { params: Promise<{ workspace: st
         setSurfaces(loaded);
         setSurfaceThemes(d.surfaceThemes ?? {});
         setSelectedThemes(d.surfaceThemes ?? {});
-        if (loaded.length > 0) setActiveSurfaceId(loaded[0]);
+        // Honour ?surface= param if valid, otherwise default to first
+        const initial = requestedSurface && loaded.includes(requestedSurface)
+          ? requestedSurface
+          : loaded[0] ?? null;
+        setActiveSurfaceId(initial);
         return loaded;
       });
 
@@ -1137,3 +1143,12 @@ export default function DesignPage({ params }: { params: Promise<{ workspace: st
     </div>
   );
 }
+
+export default function DesignPage({ params }: { params: Promise<{ workspace: string; projectId: string }> }) {
+  const { projectId } = use(params);
+  return (
+    <Suspense fallback={<div style={{ display: "flex", height: "100%", alignItems: "center", justifyContent: "center", color: "#a09a90", fontFamily: "Outfit, sans-serif", fontSize: "0.85rem" }}>Loading…</div>}>
+      <DesignPageInner projectId={projectId} />
+    </Suspense>
+  );
+}