docs: improve ai-prompt-decorator plugin docs

[Yilialinn]

Description

Improve the ai-prompt-decorator plugin doc and update the Chinese version accordingly.

Checklist

• I have explained the need for this PR and the problem it solves
• I have explained the changes or the new features added to this PR
• I have added tests corresponding to this change
• I have updated the documentation to reflect this change
• I have verified that this change is backward compatible (If not, please discuss on the APISIX mailing list first)

[Copilot]

Pull request overview

This pull request improves the documentation for the ai-prompt-decorator plugin in both English and Chinese versions. The changes enhance clarity and provide better examples for users.

Changes:

• Updated plugin descriptions to better explain functionality and purpose
• Refined attribute table with clearer field descriptions and examples
• Added comprehensive examples showing integration with ai-proxy plugin
• Replaced theoretical request body modifications with actual API response examples
• Added canonical links to external documentation

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
docs/en/latest/plugins/ai-prompt-decorator.md	Enhanced description, updated attribute table with clearer examples, added comprehensive working example with ai-proxy integration and actual API responses
docs/zh/latest/plugins/ai-prompt-decorator.md	Chinese translation of the English version improvements, maintaining consistency with English content

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[Copilot]

The description contains a duplicate word "插件插件" (plugin plugin). The first occurrence should be removed.

Suggested change

	description: ai-prompt-decorator 插件插件通过前缀和后缀附加预先设计的提示词来装饰用户向大语言模型提交的提示，从而简化 API 操作和内容生成流程。
	description: ai-prompt-decorator 插件通过前缀和后缀附加预先设计的提示词来装饰用户向大语言模型提交的提示，从而简化 API 操作和内容生成流程。

[Copilot]

There's a typo in the Chinese text. "组。" appears to be duplicated or incorrectly placed at the end of the sentence. The text should read "需要前置添加的提示对象数组。" without the extra "组。"

Suggested change

	| `prepend` | 条件性必填\* | Array | 需要前置添加的提示对象数组。组。 |
	| `prepend` | 条件性必填\* | Array | 需要前置添加的提示对象数组。 |