docs: add features chapter

[9aoy]

Summary

List the key features supported by Rstest.

Related Links

Checklist

• Tests updated (or not required).
• Documentation updated (or not required).

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[Copilot]

Pull Request Overview

This PR adds a new "Features" documentation chapter to the Rstest documentation website, providing an overview of key capabilities and features supported by the testing framework.

• Adds comprehensive features documentation in both English and Chinese
• Updates navigation metadata to include the new features page
• Documents core capabilities like Rstack ecosystem integration, multi-project testing, and DOM testing

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
website/docs/zh/guide/start/features.mdx	Chinese version of the features documentation page
website/docs/zh/guide/start/_meta.json	Updates Chinese navigation to include features page
website/docs/en/guide/start/features.mdx	English version of the features documentation page
website/docs/en/guide/start/_meta.json	Updates English navigation to include features page

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[Copilot]

The anchor link '#dom-测试' contains Chinese characters which may not work properly in URLs. Consider using an English anchor like '#dom-testing' or verify that the target page supports Chinese anchors.

Suggested change

	了解更多关于 [DOM 测试](/config/test/testEnvironment#dom-测试)。
	了解更多关于 [DOM 测试](/config/test/testEnvironment#dom-testing)。