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/repository.go

@@ -56,7 +56,7 @@ type spaceUserStore interface {
 type spacePostStore interface {
 	FindByUserID(userID uint, offset, limit int) ([]model.Post, int64, error)
 	CountUserPosts(userID uint) (int64, error)
-	GetUserStats(userID uint) (likes, favorites int64, err error)
+	GetUserStats(userID uint) (likes, favorites, reads int64, err error)
 }
 
 // postAdminStatStore AdminService 所需的帖子统计接口（ISP：2 个方法）