fix: 添加删除帖子的 mock handler

- 支持 DELETE /api/posts/:postId 请求
- 从内存存储中正确删除评论
- 修复 mock 模式下删除评论失败的问题

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/mocks/handlers/event.js

@@ -1552,7 +1552,7 @@ export const eventHandlers = [
         try {
             // 从内存存储中删除评论
             let deleted = false;
-            for (const [eventId, comments] of eventCommentsStore.entries()) {
+            for (const [eventId, comments] of commentsStore.entries()) {
                 const index = comments.findIndex(c => String(c.id) === String(postId));
                 if (index !== -1) {
                     comments.splice(index, 1);