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/post/[id]/edit/EditPostClient.tsx

@@ -1,6 +1,8 @@
 "use client";
 
 import PostComposer from "@/components/PostComposer";
+import { useUrlStyle } from "@/components/SiteBrandProvider";
+import { postPath } from "@/lib/urlStyle";
 import type { PostAttachment } from "@/lib/api";
 
 type Props = {
@@ -34,6 +36,7 @@ export default function EditPostClient({
   boardColorIndex = 0,
   boardIcon,
 }: Props) {
+  const urlStyle = useUrlStyle();
   return (
     <PostComposer
       mode="edit"
@@ -50,7 +53,7 @@ export default function EditPostClient({
       boardId={boardId}
       boardColorIndex={boardColorIndex}
       boardIcon={boardIcon}
-      cancelHref={`/post/${postId}`}
+      cancelHref={postPath(urlStyle, postId)}
     />
   );
 }