refactor: GetOverview 5 次独立查询合并为单次 GROUP BY

- 新增 PostRepo.GetOverviewByUserID 单次 CASE WHEN + GROUP BY 查询
- Service 层 GetOverview 从 5 次 DB 查询减少为 1 次
- 接口 postStore 新增 GetOverviewByUserID 声明

internal/repository/post_repo.go

@@ -108,6 +108,31 @@ func (r *PostRepo) GetUserStats(userID uint) (likes, favorites, reads int64, err
 	return s.TotalLikes, s.TotalFavorites, s.TotalReads, err
 }
 
+// overviewRow GetOverviewByUserID 单次 GROUP BY 查询结果行
+type overviewRow struct {
+	TotalPosts    int64
+	DraftCount    int64
+	PendingCount  int64
+	ApprovedCount int64
+	RejectedCount int64
+}
+
+// GetOverviewByUserID 用单次 GROUP BY 查询聚合用户各状态文章数
+func (r *PostRepo) GetOverviewByUserID(userID uint) (totalPosts, draftCount, pendingCount, approvedCount, rejectedCount int64, err error) {
+	var row overviewRow
+	err = r.db.Model(&model.Post{}).
+		Select(`
+			COUNT(*) AS total_posts,
+			COALESCE(SUM(CASE WHEN status = 'draft' THEN 1 ELSE 0 END), 0) AS draft_count,
+			COALESCE(SUM(CASE WHEN status = 'pending' THEN 1 ELSE 0 END), 0) AS pending_count,
+			COALESCE(SUM(CASE WHEN status = 'approved' THEN 1 ELSE 0 END), 0) AS approved_count,
+			COALESCE(SUM(CASE WHEN status = 'rejected' THEN 1 ELSE 0 END), 0) AS rejected_count
+		`).
+		Where("user_id = ? AND deleted_at IS NULL", userID).
+		Scan(&row).Error
+	return row.TotalPosts, row.DraftCount, row.PendingCount, row.ApprovedCount, row.RejectedCount, err
+}
+
 // FindByUserIDAndStatus 分页查询某用户指定状态的帖子（空 status=全状态）
 func (r *PostRepo) FindByUserIDAndStatus(userID uint, status string, offset, limit int) ([]model.Post, int64, error) {
 	query := r.buildQuery("", status).