fix: 实现空间 TotalReads 统计，修复 selectMention 闭包

- P0-2: posts/show.html selectMention 闭包 var→let 修复
- P0-3: GetUserStats 增加 SUM(views_count) 统计，替换硬编码 int64(0)
- 更新 Fix_List.md 标注 P0-1/2/3 已修复

internal/service/space_service.go

@@ -29,8 +29,8 @@ func (s *SpaceService) CountUserPosts(uid uint) (int64, error) {
 	return s.postRepo.CountUserPosts(uid)
 }
 
-// GetUserStats 获取用户文章统计数据（总获赞、总收藏）
-func (s *SpaceService) GetUserStats(uid uint) (likes, favorites int64, err error) {
+// GetUserStats 获取用户文章统计数据（总获赞、总收藏、总阅读）
+func (s *SpaceService) GetUserStats(uid uint) (likes, favorites, reads int64, err error) {
 	return s.postRepo.GetUserStats(uid)
 }