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/AnnouncementAdmin.tsx

@@ -13,6 +13,7 @@ import {
 import { formatDateTime, formatRelative } from "@/lib/format";
 import { toast } from "@/lib/toast";
 import ConfirmDialog from "@/components/ConfirmDialog";
+import { useUrlStyle } from "@/components/SiteBrandProvider";
 import {
   AdminEmpty,
   AdminPageHeader,
@@ -62,6 +63,7 @@ export default function AnnouncementAdmin({
 }) {
   const router = useRouter();
   const searchParams = useSearchParams();
+  const urlStyle = useUrlStyle();
   const statusFilter = readStatus(searchParams.get("status"));
   const [list, setList] = useState(initial);
   const [loadError, setLoadError] = useState(initError);
@@ -215,7 +217,7 @@ export default function AnnouncementAdmin({
                           <span className={`j13-anno-tag is-${a.tag_color}`} title={a.tag}>
                             {a.tag}
                           </span>
-                          {a.published ? <code>{announcementPublicPath(a.id)}</code> : null}
+                          {a.published ? <code>{announcementPublicPath(a.id, urlStyle)}</code> : null}
                         </p>
                         {summary ? <p className="admin-doc-excerpt" title={summary}>{summary}</p> : null}
                       </td>
@@ -241,7 +243,7 @@ export default function AnnouncementAdmin({
                           </Link>
                           {a.published ? (
                             <a
-                              href={announcementPublicPath(a.id)}
+                              href={announcementPublicPath(a.id, urlStyle)}
                               target="_blank"
                               rel="noopener noreferrer"
                               className="admin-doc-textbtn"