feat(frontend): add theme real-time sync feature

1. 新增ThemeSync组件实现站点主题色无刷新同步
2. 给获取站点设置的接口添加no-store缓存策略确保拿到最新配置
3. 调整主题应用代码的属性设置顺序避免逻辑问题

frontend/app/layout.tsx

@@ -6,6 +6,7 @@ import Header from "@/components/Header";
 import Footer from "@/components/Footer";
 import Toaster from "@/components/Toaster";
 import AccountGuard from "@/components/AccountGuard";
+import ThemeSync from "@/components/ThemeSync";
 import type { User } from "@/lib/api";
 import { getMeCached, getPublicSettingsCached } from "@/lib/serverData";
 import { TOKEN_COOKIE, REFRESH_COOKIE, authCookieHeader } from "@/lib/cookies";
@@ -104,6 +105,7 @@ export default async function RootLayout({
         <Footer />
         <Toaster />
         <AccountGuard />
+        <ThemeSync initialAccent={accent || ""} />
       </body>
     </html>
   );

frontend/components/ThemeSync.tsx

@@ -0,0 +1,70 @@
+"use client";
+
+import { useEffect, useRef } from "react";
+import { usePathname } from "next/navigation";
+import { apiGetSettings } from "@/lib/api";
+import { applyAccentTheme } from "@/lib/theme";
+
+// 站点主题色同步器：
+// 主题色由管理员在后台修改后，其他用户已打开的标签页不会因软导航重新执行根布局
+// SSR，本组件通过轮询 + 标签页重新可见/获焦时探测公开设置，发现变化即热替换
+// accent CSS 变量（复用 lib/theme 的运行时 style 节点），无需 F5 即可换肤。
+const POLL_INTERVAL_MS = 60_000;
+// 焦点/可见性事件可能短时间连续触发，限制实际请求间隔
+const MIN_FETCH_GAP_MS = 10_000;
+
+export default function ThemeSync({ initialAccent }: { initialAccent: string }) {
+  const pathname = usePathname();
+  // 当前已应用的已保存色（空串=内置默认）；与 SSR 注入的 style 节点保持一致
+  const currentRef = useRef((initialAccent || "").trim().toLowerCase());
+  const lastFetchAtRef = useRef(0);
+  const inFlightRef = useRef(false);
+
+  useEffect(() => {
+    // 外观设置页存在"未保存的本地实时预览"，该页面内暂停同步，
+    // 避免轮询结果覆盖管理员正在预览的颜色；离开页面后 effect 重跑立即对齐
+    if (pathname?.startsWith("/admin/appearance")) return;
+
+    let cancelled = false;
+
+    const sync = async () => {
+      if (inFlightRef.current) return;
+      const now = Date.now();
+      if (now - lastFetchAtRef.current < MIN_FETCH_GAP_MS) return;
+      lastFetchAtRef.current = now;
+      inFlightRef.current = true;
+      try {
+        // no-store：必须拿到管理员刚保存的最新值，不能走浏览器缓存
+        const { accent } = await apiGetSettings();
+        if (cancelled) return;
+        const next = (accent || "").trim().toLowerCase();
+        if (next !== currentRef.current) {
+          currentRef.current = next;
+          applyAccentTheme(next || null);
+        }
+      } catch {
+        // 主题同步失败静默处理，下个周期/下次回前台再试，不打扰用户
+      } finally {
+        inFlightRef.current = false;
+      }
+    };
+
+    const onActive = () => {
+      if (document.visibilityState === "visible") void sync();
+    };
+    document.addEventListener("visibilitychange", onActive);
+    window.addEventListener("focus", onActive);
+    // 离开外观页等 pathname 变化时立刻对齐一次（受 MIN_FETCH_GAP 限频）
+    void sync();
+    const timer = setInterval(() => void sync(), POLL_INTERVAL_MS);
+
+    return () => {
+      cancelled = true;
+      document.removeEventListener("visibilitychange", onActive);
+      window.removeEventListener("focus", onActive);
+      clearInterval(timer);
+    };
+  }, [pathname]);
+
+  return null;
+}

frontend/lib/api.ts

@@ -949,7 +949,8 @@ export async function apiAdminSetUserBan(
 // ===== 站点外观设置 =====
 
 export async function apiGetSettings(): Promise<PublicSettings> {
-  const res = await fetchWithRefresh("/api/settings", { method: "GET" });
+  // no-store：主题同步轮询必须读到管理员刚保存的最新配色，不走浏览器缓存
+  const res = await fetchWithRefresh("/api/settings", { method: "GET", cache: "no-store" });
   if (!res.ok) throw new Error("获取站点设置失败");
   return res.json();
 }

frontend/lib/theme.ts

@@ -236,8 +236,8 @@ export function applyAccentTheme(input: string | null): void {
   if (!el) {
     el = document.createElement("style");
     el.id = STYLE_ELEMENT_ID;
-    el.setAttribute("data-accent-source", "runtime");
     document.head.appendChild(el);
   }
+  el.setAttribute("data-accent-source", "runtime");
   el.textContent = css;
 }