refactor(entity): 优化实体类字段描述

- 更新 image 实体类字段描述，明确各字段含义
- 修改 MarkdownFile 实体类字段描述，提高字段可理解性

biji-houdaun/src/main/java/com/test/bijihoudaun/entity/Image.java

@@ -16,27 +16,28 @@ public class Image {
     @Schema(description = "图片id",implementation = Long.class)
     @TableId(type = IdType.AUTO)
     private Long id;
-    @Schema(description = "图片名称",implementation = Long.class  )
+    @Schema(description = "外键，关联用户ID，标识图片所有者\n",implementation = Long.class  )
     private Long userId;
-    @Schema(description = "图片名称",implementation = Long.class  )
+    @Schema(description = " 外键，关联Markdown文件ID，标识图片所属文档",implementation = Long.class  )
     private Long markdownId;
 
-    @Schema(description = "图片名称",implementation = String.class  )
+    @Schema(description = "原始文件名（用户上传时的文件名）",implementation = String.class  )
     @TableField("original_name")
     private String originalName;
 
-    @Schema(description = "图片名称",implementation = String.class  )
+    @Schema(description = "存储文件名（系统生成的唯一文件名）",implementation = String.class  )
     @TableField("stored_name")
     private String storedName;
 
-    @Schema(description = "图片名称",implementation = String.class  )
+    @Schema(description = " 图片访问URL",implementation = String.class  )
     private String url;
-    @Schema(description = "图片大小",implementation = Long.class  )
+    @Schema(description = "图片大小（字节）",implementation = Long.class  )
     private Long size;
 
-    @Schema(description = "图片类型",implementation = String.class  )
+    @Schema(description = "图片MIME类型（如image/jpeg）",implementation = String.class  )
     @TableField("content_type")
     private String contentType;
 
+    @Schema(description = "图片上传时间",implementation = LocalDateTime.class  )
     private LocalDateTime createdAt;
 }