feat: 评论系统补充功能完成——图片上传、后台管理、通知跳转高亮

- 评论图片上传（LV4+，经验≥1500），JPEG/PNG 自动转 WebP，二进制搜索质量优化
- 后台评论管理页面，支持关键词搜索、分页、删除，侧边栏新增入口
- 通知跳转高亮：评论通知 RelatedID 改为 postID，消息页链接到 #comments，前端自动滚动
- 新增 adminCommentUseCase/commentStore 接口（遵循 ISP），AdminCommentRow 移至 model 层
- 前端 @mention 联想/图片上传光标插入/评论展开收起/内联回复交互完善

internal/repository/comment_repo.go

@@ -248,3 +248,31 @@ func (r *CommentRepo) FindPostAuthorID(postID uint) (uint, error) {
 	err := r.db.Table("posts").Select("user_id").Where("id = ?", postID).Scan(&authorID).Error
 	return authorID, err
 }
+
+// ListAllComments 后台评论列表（支持关键词搜索、分页）
+func (r *CommentRepo) ListAllComments(keyword string, showDeleted bool, offset, limit int) ([]model.AdminCommentRow, int64, error) {
+	var total int64
+	q := r.db.Table("comments").
+		Joins("LEFT JOIN users ON users.uid = comments.user_id").
+		Joins("LEFT JOIN posts ON posts.id = comments.post_id")
+
+	if !showDeleted {
+		q = q.Where("comments.is_deleted = false")
+	}
+	if keyword != "" {
+		like := "%" + keyword + "%"
+		q = q.Where("comments.body LIKE ? OR users.username LIKE ? OR posts.title LIKE ?", like, like, like)
+	}
+
+	if err := q.Count(&total).Error; err != nil {
+		return nil, 0, err
+	}
+
+	var rows []model.AdminCommentRow
+	err := q.
+		Select("comments.id, comments.post_id, posts.title as post_title, comments.body, users.username as author_name, comments.is_deleted, comments.created_at, comments.updated_at").
+		Order("comments.created_at DESC").
+		Offset(offset).Limit(limit).
+		Scan(&rows).Error
+	return rows, total, err
+}