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/controller/interfaces.go

@@ -55,7 +55,7 @@ type spaceUseCase interface {
 	GetSpaceUser(uid uint) (*model.User, error)
 	GetPostsByUser(uid uint, page, pageSize int) ([]model.Post, int64, error)
 	CountUserPosts(uid uint) (int64, error)
-	GetUserStats(uid uint) (likes, favorites int64, err error)
+	GetUserStats(uid uint) (likes, favorites, reads int64, err error)
 	UpdateUser(user *model.User) error
 }