/** 同一套规则用于首屏内联启动和运行时切换，避免两次绘制使用不同主题。 */
export function applyTheme(mode) {
  if (mode === undefined) {
    try {
      mode = localStorage.getItem("theme");
    } catch {}
  }
  if (mode !== "light" && mode !== "dark") mode = "auto";
  const dark =
    mode === "dark" ||
    (mode === "auto" && matchMedia("(prefers-color-scheme: dark)").matches);
  document.documentElement.classList.toggle("app-dark", dark);
  document.documentElement.style.colorScheme = dark ? "dark" : "light";
  return { mode, dark };
}