fix: use server.localhost subdomain for server-ui (same /assets conflict)

Server UI assets also use absolute /assets/* paths that conflict with
the SPA catch-all. Same fix as Logto: Host-based routing at
server.localhost gives it its own namespace.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/src/components/Layout.tsx

@@ -162,7 +162,7 @@ export function Layout() {
         <Sidebar.FooterLink
           icon={<ObsIcon />}
           label="View Dashboard"
-          onClick={() => window.open('/server/', '_blank', 'noopener')}
+          onClick={() => window.open(`http://server.${window.location.hostname}`, '_blank', 'noopener')}
         />
 
         {/* User info + logout */}