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/pages/PagesAdmin.tsx

@@ -7,6 +7,7 @@ import { Ellipsis, ExternalLink, FileText, Plus } from "lucide-react";
 import { apiAdminDeleteSitePage, type SitePage } from "@/lib/api";
 import { formatDateTime, formatRelative } from "@/lib/format";
 import { sitePagePublicPath } from "@/lib/sitePagePath";
+import { useUrlStyle } from "@/components/SiteBrandProvider";
 import { toast } from "@/lib/toast";
 import ConfirmDialog from "@/components/ConfirmDialog";
 import {
@@ -50,6 +51,7 @@ export default function PagesAdmin({
 }) {
   const router = useRouter();
   const searchParams = useSearchParams();
+  const urlStyle = useUrlStyle();
   const statusFilter = readStatus(searchParams.get("status"));
   const [list, setList] = useState(initial);
   const [loadError] = useState(initError);
@@ -166,7 +168,7 @@ export default function PagesAdmin({
               <tbody>
                 {filtered.map((p) => {
                   const updated = p.updated_at || "";
-                  const path = sitePagePublicPath(p.slug);
+                  const path = sitePagePublicPath(p.slug, urlStyle);
                   return (
                     <tr key={p.id}>
                       <td data-label="页面">