fix(customs): 对齐 ExpressionRecognition 注册方式与 README 格式

[overflow65537]

Summary by Sourcery

使 ExpressionRecognition 自定义识别器的注册方式与文档中描述的用法保持一致，并更新 README 以匹配当前的管道配置和表达式语义。

增强内容：

• 使用 AgentServer 的 custom_recognition 装饰器，直接在类上注册 ExpressionRecognition，以符合预期用法。

文档更新：

• 重写 ExpressionRecognition 的 README，重点放在面向使用场景的示例上，澄清表达式语法和参数，并使注册方式与管道示例对齐，以匹配当前实现。

Original summary in English

Summary by Sourcery

Align the ExpressionRecognition custom recognizer’s registration with the documented usage and refresh the README to match the current pipeline configuration and expression semantics.

Enhancements:

• Register ExpressionRecognition directly on the class using the AgentServer custom_recognition decorator to match expected usage.

Documentation:

• Rewrite the ExpressionRecognition README to focus on usage-oriented examples, clarify expression syntax and parameters, and align registration and pipeline samples with the current implementation.

[sourcery-ai]

嗨——我已经审查了你的改动，一切看起来都很棒！

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Original comment in English

Hey - I've reviewed your changes and they look great!

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