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/announcement/[id]/page.tsx

@@ -17,6 +17,7 @@ import {
   SiteDocMasthead,
 } from "@/components/site-doc";
 import { requestCanonical } from "@/lib/canonicalMeta";
+import { announcementPath } from "@/lib/urlStyle";
 import { webPageJsonLd } from "@/lib/jsonLd";
 import JsonLd from "@/components/JsonLd";
 
@@ -28,6 +29,7 @@ export async function generateMetadata({ params }: PageProps): Promise<Metadata>
   const { id } = await params;
   const data = await fetchAnnouncementDetail(id).catch(() => null);
   if (!data) return { title: "公告不存在" };
+  const urlStyle = (await getPublicSettingsCached()).url_style;
   return {
     title: data.announcement.title,
     description: `站点公告 · ${data.announcement.tag}`,
@@ -37,7 +39,7 @@ export async function generateMetadata({ params }: PageProps): Promise<Metadata>
       type: "article",
       publishedTime: data.announcement.created_at,
     },
-    ...(await requestCanonical(`/announcement/${data.announcement.id}`)),
+    ...(await requestCanonical(announcementPath(urlStyle, data.announcement.id))),
   };
 }
 
@@ -59,6 +61,7 @@ export default async function AnnouncementPage({ params }: PageProps) {
   const announcements = overview?.announcements ?? [];
   const canManagePages = !!me.user && isAdminOrAbove(me.user.role);
   const siteLead = settings.site_description?.trim() || undefined;
+  const urlStyle = settings.url_style;
   const toc = extractToc(a.content);
   const headingToc = markdownHeadingToc(toc);
   const readingMinutes = estimateReadingMinutes(a.content, a.title.length);
@@ -77,7 +80,7 @@ export default async function AnnouncementPage({ params }: PageProps) {
   const jsonLd = webPageJsonLd({
     type: "Article",
     name: a.title,
-    path: `/announcement/${a.id}`,
+    path: announcementPath(urlStyle, a.id),
     datePublished: a.created_at,
     dateModified: a.updated_at,
     articleSection: "站点公告",