refactor: Private bool → Visibility string 支持多种可见范围 (#464)

* docs: 更新 API 文档以包含 private 参数的用途和可选性。

* refactor: visibility 功能从 Private bool 重构为 Visibility string

将发布时可见范围参数从 `Private bool` 改为 `Visibility string`，
支持三种选项：公开可见(默认)、仅自己可见、仅互关好友可见。

- 使用精确 CSS selector 替代遍历 span/label/div 的宽泛选择器
- 新增参数校验，不支持的选项直接返回错误
- 更新 API 文档和 MCP jsonschema 描述
- 与 upstream IsOriginal(原创声明) 功能共存

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: yryangang <dd101bb@qq.com>
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

docs/API.md

@@ -171,7 +171,8 @@ Content-Type: application/json
     "http://example.com/image1.jpg",
     "http://example.com/image2.jpg"
   ],
-  "tags": ["标签1", "标签2"]
+  "tags": ["标签1", "标签2"],
+  "visibility": "公开可见"
 }
 ```
 
@@ -180,6 +181,7 @@ Content-Type: application/json
 - `content` (string, required): 笔记内容
 - `images` (array, required): 图片URL数组，至少包含一张图片
 - `tags` (array, optional): 标签数组
+- `visibility` (string, optional): 可见范围，支持: `公开可见`(默认)、`仅自己可见`、`仅互关好友可见`。不填则默认公开可见
 
 **响应**
 ```json
@@ -212,7 +214,8 @@ Content-Type: application/json
   "title": "视频标题",
   "content": "视频内容描述",
   "video": "/Users/username/Videos/video.mp4",
-  "tags": ["标签1", "标签2"]
+  "tags": ["标签1", "标签2"],
+  "visibility": "公开可见"
 }
 ```
 
@@ -221,6 +224,7 @@ Content-Type: application/json
 - `content` (string, required): 视频内容描述
 - `video` (string, required): 本地视频文件绝对路径
 - `tags` (array, optional): 标签数组
+- `visibility` (string, optional): 可见范围，支持: `公开可见`(默认)、`仅自己可见`、`仅互关好友可见`。不填则默认公开可见
 
 **响应**
 ```json