chore: 去掉未上线前的旧兼容垫片，板块流收口到首页

鉴权只认 cookie、SEO 只走 Next、sort 与推荐对齐；删除 Bearer、Go sitemap、post_type 回填等冗余路径。

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/app/sitemap.ts

@@ -1,5 +1,5 @@
 import type { MetadataRoute } from "next";
-import { fetchPosts, fetchBoards } from "@/lib/api";
+import { fetchPosts } from "@/lib/api";
 
 export default async function sitemap(): Promise<MetadataRoute.Sitemap> {
   const baseUrl = "http://localhost:3000";
@@ -8,16 +8,6 @@ export default async function sitemap(): Promise<MetadataRoute.Sitemap> {
   ];
 
   try {
-    const { boards } = await fetchBoards();
-    for (const board of boards) {
-      entries.push({
-        url: `${baseUrl}/board/${board.id}`,
-        lastModified: new Date(),
-        changeFrequency: "daily",
-        priority: 0.8,
-      });
-    }
-
     const { posts } = await fetchPosts(1, 100);
     for (const post of posts) {
       entries.push({