mcp: add image url support (#1)

* refactor: remove redundant validation in service and clean up code

- Remove validatePublishRequest function as gin binding already handles validation
- Remove unused errors import
- Simplify PublishContent method by relying on gin's built-in validation
- Add comprehensive image processing support with URL download capability

* 添加 MCP 说明文档，完善教程

README.md

@@ -14,6 +14,38 @@ MCP for xiaohongshu.com
 go run cmd/login/main.go
 ```
 
-### 发布
+### 启动 MCP 服务
 
 启动 xiaohongshu-mcp 服务。
+
+```bash
+go run . -headless=false
+```
+
+## 验证 MCP
+
+```bash
+npx @modelcontextprotocol/inspector
+```
+
+![运行 Inspector](./assets/mcp-inspector.png)
+
+运行后，打开红色标记的链接，配置 MCP inspector，输入 `http://localhost:18060/mcp` ，点击 `Connect` 按钮。
+
+## 使用 MCP 发布
+
+### 检查登录状态
+
+<video width="600" controls>
+  <source src="./assets/check_login.mp4" type="video/mp4">
+  Your browser does not support the video tag.
+</video>
+
+### 发布图文
+
+示例中是从 https://unsplash.com/ 中随机找了个图片做测试。
+
+<video width="600" controls>
+  <source src="./assets/inspect_mcp_publish.mp4" type="video/mp4">
+  Your browser does not support the video tag.
+</video>