feat: 评论/帖子编辑历史与编辑标记，内容锁定

- 新增 smartDiff 差异计算与 EditHistoryModal 编辑历史弹窗，替换原 CommentEditHistoryModal
- 新增 PostEditedMark 编辑标记展示
- 新增内容锁定机制（content_lock）防止并发编辑冲突
- 审核与通知服务适配

backend/handler/comment.go

@@ -2,6 +2,7 @@ package handler
 
 import (
 	"errors"
+	"fmt"
 	"net/http"
 	"strconv"
 
@@ -83,7 +84,7 @@ func (h *Handlers) PostComments(c *gin.Context) {
 
 // CreateCommentRequest 评论请求
 type CreateCommentRequest struct {
-	Content  string `json:"content" binding:"required,min=1"`
+	Content  string `json:"content" binding:"required,min=1,max=5000"`
 	ParentID *uint  `json:"parent_id"` // 非空 = 回复该评论（发为其子评论）
 }
 
@@ -109,11 +110,24 @@ func (h *Handlers) CreateComment(c *gin.Context) {
 	}
 	// staff 直发；已过审用户在站点开启免审时可直发；其余进待审队列（通过时才发业务通知）
 	status := h.resolvePublishStatus(claims.ID, claims.Role)
-	comment, parent, err := h.Comment.Create(claims.ID, uint(id), req.Content, req.ParentID, status)
+	comment, parent, necroPoints, err := h.Comment.Create(claims.ID, uint(id), req.Content, req.ParentID, status, model.Role(claims.Role))
 	if err != nil {
-		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+		switch {
+		case errors.Is(err, service.ErrPostReplyLocked):
+			c.JSON(http.StatusForbidden, gin.H{"error": err.Error()})
+		case errors.Is(err, service.ErrInsufficientPoints):
+			// 旧帖回复扣分余额不足（文案含具体规则）
+			c.JSON(http.StatusPaymentRequired, gin.H{"error": err.Error()})
+		default:
+			c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
+		}
 		return
 	}
+	// 旧帖回复扣分：系统提醒本人（ActorID=0，不经过自我通知过滤）
+	if necroPoints > 0 {
+		h.Notification.CreateSystem(claims.ID, model.NotificationTypeNecroReply, uint(id), comment.ID,
+			fmt.Sprintf("您回复了长期没有新回复的旧帖，已扣除 %d 积分", necroPoints))
+	}
 	if comment.Status == model.ContentStatusPublished {
 		if parent == nil {
 			// 主评论：通知帖子作者（排除自己评论自己的帖子）
@@ -146,7 +160,7 @@ func (h *Handlers) UpdateComment(c *gin.Context) {
 		return
 	}
 	var body struct {
-		Content string `json:"content"`
+		Content string `json:"content" binding:"omitempty,min=1,max=5000"`
 	}
 	if err := c.ShouldBindJSON(&body); err != nil {
 		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
@@ -157,7 +171,9 @@ func (h *Handlers) UpdateComment(c *gin.Context) {
 		switch {
 		case errors.Is(err, service.ErrCommentNotFound):
 			c.JSON(http.StatusNotFound, gin.H{"error": err.Error()})
-		case errors.Is(err, service.ErrCommentForbidden):
+		case errors.Is(err, service.ErrCommentForbidden),
+			errors.Is(err, service.ErrCommentPostLocked),
+			errors.Is(err, service.ErrCommentEditLocked):
 			c.JSON(http.StatusForbidden, gin.H{"error": err.Error()})
 		case errors.Is(err, service.ErrCommentDeleted),
 			errors.Is(err, service.ErrCommentNotChanged):
@@ -256,3 +272,39 @@ func (h *Handlers) PurgeComment(c *gin.Context) {
 	}
 	c.JSON(http.StatusOK, gin.H{"message": "已彻底删除"})
 }
+
+// CommentEditHistory 评论编辑历史（登录即可见；分页）
+func (h *Handlers) CommentEditHistory(c *gin.Context) {
+	claims := middleware.CurrentUser(c)
+	cid, err := strconv.ParseUint(c.Param("cid"), 10, 64)
+	if err != nil || cid == 0 {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "无效的评论 ID"})
+		return
+	}
+	page, _ := strconv.Atoi(c.DefaultQuery("page", "1"))
+	size, _ := strconv.Atoi(c.DefaultQuery("size", "10"))
+	items, total, err := h.Comment.ListEditHistory(h.loadActor(claims.ID), uint(cid), page, size)
+	if err != nil {
+		switch {
+		case errors.Is(err, service.ErrCommentNotFound):
+			c.JSON(http.StatusNotFound, gin.H{"error": err.Error()})
+		case errors.Is(err, service.ErrCommentForbidden):
+			c.JSON(http.StatusForbidden, gin.H{"error": err.Error()})
+		default:
+			c.JSON(http.StatusInternalServerError, gin.H{"error": "获取编辑历史失败"})
+		}
+		return
+	}
+	if page < 1 {
+		page = 1
+	}
+	if size < 1 || size > 50 {
+		size = 10
+	}
+	c.JSON(http.StatusOK, gin.H{
+		"items": items,
+		"total": total,
+		"page":  page,
+		"size":  size,
+	})
+}