Setup Co-op translator

[zahlekhan]

Is your feature request related to a problem? Please describe.
OpenUI's documentation site and README are currently English-only. This limits accessibility for Chinese-speaking developers, who represent a significant portion of the AI/LLM developer community.

Describe the solution you'd like
Set up Co-op Translator to provide automated, synchronized Chinese (Simplified) translations for the project. This includes:

1. Infrastructure setup — Integrate Co-op Translator into the repository with GitHub Actions so translations stay in sync as source content changes.
2. Documentation site translation — Translate the docs site (docs/) content into Chinese (Simplified).
3. README translation — Translate the root README.md into Chinese, stored under a translations/zh/ directory.
4. Scalable i18n foundation — The Co-op Translator setup should make it straightforward to add more languages in the future by simply updating the language list.

Describe alternatives you've considered

• Manual one-time translation of all docs, but this becomes stale as the English docs evolve and requires ongoing effort to maintain.
• Using a docs platform with built-in i18n (e.g., Docusaurus i18n), but the current docs site uses Fumadocs/Next.js and switching would be a larger effort.
• Using a different translation tool, but Co-op Translator is purpose-built for GitHub educational/OSS content and handles Markdown, images, and notebooks natively.

Additional context
Co-op Translator reference: https://github.com/Azure/co-op-translator. It supports CLI usage, Docker, and GitHub Actions for CI-based translation. The initial target is Chinese (Simplified), but the setup should allow adding more languages (e.g., Japanese, Korean) later with minimal effort.

[shogun444]

Hi @zahlekhan I've opened a PR implementing the Co-op Translator setup for this issue.

PR: #310

Happy to make adjustments if anything needs to be changed.