Translate AI docs and assistant API updates to es, fr, zh

[mintlify]

Summary

Translates changes from commits since the last translation PR (#4647) into Spanish, French, and Chinese:

• ai/llmstxt.mdx: Added .well-known path mention, HTTP headers discovery section, .md extensions in page links, separated OpenAPI/AsyncAPI spec sections in example, repositioned structured approach paragraph
• ai/markdown-export.mdx: Added new "Accept header" section for text/markdown and text/plain content negotiation
• ai/skillmd.mdx: Removed "(with caching disabled)" from reverse proxy note, added "Skills discovery endpoints" section with skills index and individual skill file endpoints
• api/assistant/create-assistant-message-v2.mdx: Fixed internal link from /api-reference/ to /api/
• api/assistant/create-assistant-message.mdx: Fixed internal link from /api-reference/ to /api/

No docs.json or API spec file changes were needed.

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Note

Low Risk
Low risk documentation-only updates (translations/content tweaks) with no runtime or API behavior changes.

Overview
Updates the Spanish/French/Chinese AI docs to reflect recent llms.txt and Markdown-export capabilities, including .well-known hosting, HTTP header-based discovery, .md page links, and clearer OpenAPI/AsyncAPI sections.

Adds guidance on requesting Markdown via the Accept: text/markdown/text/plain headers, documents /.well-known/skills/ discovery endpoints for skill.md, removes the “disable caching” note for reverse proxies, and fixes internal assistant API doc links from /api-reference/ to /api/.

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