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

components/layout/vibn-sidebar.tsx

@@ -338,12 +338,12 @@ export function VIBNSidebar({ workspace }: VIBNSidebarProps) {
                   key={s}
                   icon={SURFACE_ICONS[s] ?? "◌"}
                   label={SURFACE_LABELS[s] ?? s}
-                  href={`${base}/design`}
+                  href={`${base}/design?surface=${encodeURIComponent(s)}`}
                   collapsed={collapsed}
                 />
               ))
             ) : (
-              <SectionRow icon="◌" label="Not configured" dim collapsed={collapsed} />
+              <SectionRow icon="◌" label="Not configured" dim href={`${base}/design`} collapsed={collapsed} />
             )}
 
             <SectionDivider />