docs: add AI Router to AI Cloud Platform

[airouter-dev]

Tool recommendation

• Tool name and URL: AI Router — https://ai-router.dev
• Core functionality: Independent OpenAI-compatible API service for developers. It supports a personal API key, configurable base URL, per-key usage visibility, and current model discovery through /v1/models.
• Target users: Developers and programmers.
• Pricing: Paid. This submission makes no trial, credit, fixed-model, or reliability claim.
• Localization: The English entry uses the root URL; the Chinese entry uses https://ai-router.dev/cn.
• Disclosure: I operate AI Router. It is not affiliated with OpenAI.

[github-actions]

Hi @airouter-dev! 👋

Thank you for your pull request! We're excited to review your contribution.

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We'll review your PR as soon as possible! 🚀