fix: 默认板块仅在空库播种，改名后重启不再复活

backend/model/db.go

@@ -382,20 +382,23 @@ func backfillBoardDefaults(db *gorm.DB) {
 	}
 }
 
-// seedDefaultBoards 写入默认板块
+// seedDefaultBoards 仅在板块表为空（全新站点首启）时写入默认板块。
+// 曾按「名字是否存在」补种：站长改名板块后每次重启都会复活一套默认板块
+// （真实事故：0.2.1 重启后默认 4 板块重现）。表里已有任何未删除板块即视为已初始化。
 func seedDefaultBoards(db *gorm.DB) {
+	var count int64
+	db.Model(&Board{}).Count(&count)
+	if count > 0 {
+		return
+	}
 	defaults := []Board{
 		{Name: "综合讨论", Description: "什么都可以聊", Icon: "message-circle", SortOrder: 1, PostPolicy: BoardPostPolicyAll, Visible: true},
 		{Name: "技术分享", Description: "分享技术心得与问题", Icon: "code", SortOrder: 2, PostPolicy: BoardPostPolicyAll, Visible: true},
 		{Name: "问答求助", Description: "提问与解答", Icon: "help-circle", SortOrder: 3, PostPolicy: BoardPostPolicyAll, Visible: true},
 		{Name: "闲聊灌水", Description: "轻松闲聊", Icon: "coffee", SortOrder: 4, PostPolicy: BoardPostPolicyAll, Visible: true},
 	}
-	for _, b := range defaults {
-		var count int64
-		db.Model(&Board{}).Where("name = ?", b.Name).Count(&count)
-		if count == 0 {
-			_ = db.Create(&b).Error
-		}
+	for i := range defaults {
+		_ = db.Create(&defaults[i]).Error
 	}
 }