feat(admin): add opt-in server timing metrics

Co-authored-by: multica-agent <github@multica.ai>

frontend/src/api/adminUIRequest.ts

@@ -0,0 +1,27 @@
+export const ADMIN_UI_REQUEST_HEADER = 'X-Admin-UI-Request'
+
+function isAdminPath(path: string): boolean {
+  return (
+    path === '/admin' ||
+    path.startsWith('/admin/') ||
+    path === '/api/v1/admin' ||
+    path.startsWith('/api/v1/admin/')
+  )
+}
+
+function requestPath(rawURL: string): string {
+  const value = rawURL.trim()
+  if (!value) return ''
+  try {
+    const origin = typeof window !== 'undefined' ? window.location.origin : 'http://localhost'
+    return new URL(value, origin).pathname
+  } catch {
+    return value.split(/[?#]/, 1)[0]
+  }
+}
+
+export function shouldMarkAdminUIRequest(requestURL: string, pagePath?: string): boolean {
+  const currentPath =
+    pagePath ?? (typeof window !== 'undefined' ? window.location.pathname : '')
+  return isAdminPath(requestPath(requestURL)) || isAdminPath(currentPath)
+}