feat(moderation): 帖评删除占位感知与硬删清场

管理删帖须填类型与理由并展示专用页；评论软删占位、版主可硬删不占楼。

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

backend/handler/comment.go

@@ -66,6 +66,13 @@ func (h *Handlers) CreateComment(c *gin.Context) {
 		c.JSON(http.StatusBadRequest, gin.H{"error": "无效的帖子 ID"})
 		return
 	}
+	if allow, err := h.Setting.AllowComments(); err != nil {
+		c.JSON(http.StatusInternalServerError, gin.H{"error": "评论暂时不可用"})
+		return
+	} else if !allow {
+		c.JSON(http.StatusForbidden, gin.H{"error": "站点已关闭评论"})
+		return
+	}
 	var req CreateCommentRequest
 	if err := c.ShouldBindJSON(&req); err != nil {
 		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
@@ -99,7 +106,7 @@ func (h *Handlers) CreateComment(c *gin.Context) {
 	c.JSON(http.StatusOK, gin.H{"comment": comment})
 }
 
-// DeleteComment 删除评论
+// DeleteComment 软删评论（占位）
 func (h *Handlers) DeleteComment(c *gin.Context) {
 	claims := middleware.CurrentUser(c)
 	cid, err := strconv.ParseUint(c.Param("cid"), 10, 64)
@@ -120,3 +127,25 @@ func (h *Handlers) DeleteComment(c *gin.Context) {
 	}
 	c.JSON(http.StatusOK, gin.H{"message": "已删除"})
 }
+
+// PurgeComment 硬删评论及子树（仅版主；不占位）
+func (h *Handlers) PurgeComment(c *gin.Context) {
+	claims := middleware.CurrentUser(c)
+	cid, err := strconv.ParseUint(c.Param("cid"), 10, 64)
+	if err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "无效的评论 ID"})
+		return
+	}
+	if err := h.Comment.Purge(h.loadActor(claims.ID), uint(cid), claims.ID); 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.StatusBadRequest, gin.H{"error": err.Error()})
+		}
+		return
+	}
+	c.JSON(http.StatusOK, gin.H{"message": "已彻底删除"})
+}