修复首屏：增加预加载占位并提前恢复主题

app/utils/theme-appearance.js

@@ -0,0 +1,15 @@
+/** 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 };
+}