feat(notif): 点赞通知延迟落库，短时取消不打扰作者

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/service/notification.go

@@ -1,10 +1,16 @@
 package service
 
 import (
+	"log"
+	"time"
+
 	"github.com/freefire/jiang13-bbs/model"
 	"gorm.io/gorm"
 )
 
+// LikeNotifyDelay 点赞通知冷却：未满该时长即取消点赞则不通知作者
+const LikeNotifyDelay = time.Minute
+
 // NotificationService 通知服务
 type NotificationService struct {
 	db *gorm.DB
@@ -16,6 +22,57 @@ func NewNotificationService(db *gorm.DB) *NotificationService {
 	return &NotificationService{db: db}
 }
 
+// FlushPendingLikeNotifications 将已冷却且仍有效的点赞落为通知（误赞撤回不会进入此处）。
+func (s *NotificationService) FlushPendingLikeNotifications(limit int) {
+	if limit < 1 {
+		limit = 50
+	}
+	cutoff := time.Now().Add(-LikeNotifyDelay)
+	type pendingLike struct {
+		PostID   uint
+		UserID   uint
+		AuthorID uint
+	}
+	var rows []pendingLike
+	err := s.db.Raw(`
+		SELECT l.post_id AS post_id, l.user_id AS user_id, p.user_id AS author_id
+		FROM likes l
+		INNER JOIN posts p ON p.id = l.post_id
+		WHERE l.created_at <= ?
+		  AND p.deleted_at IS NULL
+		  AND p.status = ?
+		  AND l.user_id <> p.user_id
+		  AND NOT EXISTS (
+			SELECT 1 FROM notifications n
+			WHERE n.type = ?
+			  AND n.actor_id = l.user_id
+			  AND n.post_id = l.post_id
+			  AND n.user_id = p.user_id
+			  AND n.created_at >= l.created_at
+		  )
+		ORDER BY l.created_at ASC
+		LIMIT ?
+	`, cutoff, model.ContentStatusPublished, model.NotificationTypeLike, limit).Scan(&rows).Error
+	if err != nil {
+		log.Printf("[notif] 扫描待发点赞通知失败: %v", err)
+		return
+	}
+	for _, row := range rows {
+		s.Create(row.AuthorID, row.UserID, model.NotificationTypeLike, row.PostID, 0, "")
+	}
+}
+
+// StartLikeNotifyFlusher 周期落库冷却后的点赞通知
+func StartLikeNotifyFlusher(s *NotificationService) {
+	go func() {
+		t := time.NewTicker(20 * time.Second)
+		defer t.Stop()
+		for range t.C {
+			s.FlushPendingLikeNotifications(50)
+		}
+	}()
+}
+
 // Create 创建通知（actorID == userID 时跳过，不通知自己）
 func (s *NotificationService) Create(userID, actorID uint, notifType string, postID, commentID uint, content string) {
 	if userID == 0 || actorID == 0 || userID == actorID {