feat: 可配置站点 URL 风格

- 新增 urlStyle 工具与测试：postPath/userPath/sitePagePath 统一生成链接
- 管理端新增 UrlStylePanel 设置面板，settings 服务与 handler 适配
- 全站路由链接与 JSON-LD/sitemap 切换为统一 URL 生成
- middleware 与相关组件适配

frontend/app/admin/announcements/AnnouncementComposeClient.tsx

@@ -15,6 +15,7 @@ import { toast } from "@/lib/toast";
 import MarkdownEditor from "@/components/MarkdownEditor";
 import { AdminField, AdminSegmented, AdminStatusChip, AdminSwitch } from "@/components/admin";
 import ConfirmDialog from "@/components/ConfirmDialog";
+import { useUrlStyle } from "@/components/SiteBrandProvider";
 import useUnsavedGuard from "@/hooks/useUnsavedGuard";
 import { ANNOUNCEMENT_COLORS, announcementPublicPath } from "./announcementColors";
 
@@ -117,6 +118,7 @@ export default function AnnouncementComposeClient({
 }) {
   const router = useRouter();
   const searchParams = useSearchParams();
+  const urlStyle = useUrlStyle();
   const status = readStatus(searchParams.get("status"));
   const backHref = listHref(status);
   const loaded = useMemo(() => toForm(initial), [initial]);
@@ -146,7 +148,7 @@ export default function AnnouncementComposeClient({
   };
 
   const canViewOnline = saved?.published === true && saved.id > 0;
-  const publicPath = saved ? announcementPublicPath(saved.id) : "";
+  const publicPath = saved ? announcementPublicPath(saved.id, urlStyle) : "";
 
   async function commit() {
     if (saving) return;
@@ -227,7 +229,7 @@ export default function AnnouncementComposeClient({
 
   async function copyAddress() {
     if (!saved) return;
-    const url = `${(origin || window.location.origin).replace(/\/$/, "")}${announcementPublicPath(saved.id)}`;
+    const url = `${(origin || window.location.origin).replace(/\/$/, "")}${announcementPublicPath(saved.id, urlStyle)}`;
     try {
       await navigator.clipboard.writeText(url);
       toast("已复制访问地址", "ok");