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>
   );