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/components/PostAttachments.tsx

@@ -12,6 +12,8 @@ import {
 import { fileExtBadge, fileKind } from "@/lib/fileKind";
 import { toast } from "@/lib/toast";
 import Modal from "@/components/Modal";
+import { postPath } from "@/lib/urlStyle";
+import { useUrlStyle } from "@/components/SiteBrandProvider";
 
 function formatSize(n: number) {
   if (n < 1024) return `${n} B`;
@@ -86,7 +88,8 @@ export default function PostAttachments({
   loggedIn: boolean;
 }) {
   const router = useRouter();
-  const loginHref = `/login?redirect=${encodeURIComponent(`/post/${postId}`)}`;
+  const urlStyle = useUrlStyle();
+  const loginHref = `/login?redirect=${encodeURIComponent(postPath(urlStyle, postId))}`;
   const [busyId, setBusyId] = useState<number | null>(null);
   const [pending, setPending] = useState<PostAttachment | null>(null);
   const [unlockedIds, setUnlockedIds] = useState<number[]>([]);