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/lib/postMeta.ts

@@ -23,7 +23,7 @@ export const BOUNTY_EXPIRE_DAYS = [3, 7, 14, 30] as const;
 export const LOTTERY_EXPIRE_DAYS = [1, 3, 7, 14] as const;
 
 export function normalizePostType(t?: string): PostTypeValue {
-  if (t === "normal" || !t) return "discussion";
+  if (!t) return "discussion";
   if (POST_TYPES.some((x) => x.value === t)) return t as PostTypeValue;
   return "discussion";
 }