Add Chinese (cn) documentation pages and navigation

[Rferdana]

Motivation

• Provide a full set of Chinese-localized documentation pages to support Chinese-speaking developers and users.
• Expose the new cn documentation in the site navigation so the localized content is discoverable.

Description

• Added multiple Chinese MDX pages under cn/learn, cn/builders, cn/users, cn/resources, and cn/home/governance covering protocol overview, tokenomics, revenue model, bonding curve economics, developer guides, user guides, FAQ, media assets, smart contracts, and governance content.
• Created cn-scoped pages such as cn/learn/protocol-overview.mdx, cn/builders/getting-started.mdx, cn/users/buy-and-trade.mdx, cn/resources/faq.mdx, and others to provide localized guidance and references.
• Updated docs.json to register a new language entry for cn and add tabs/groups/pages so the new Chinese pages appear in the documentation navigation.
• Minor metadata/frontmatter included in each MDX file (title/description) to integrate with the documentation layout and cards.

Testing

• Built the documentation site locally with yarn build and verified the build completed without errors.
• Verified the updated docs.json loads the cn language blocks and that the new pages are referenced in the navigation during the local site preview.
• No automated unit tests were modified by these documentation additions.

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Codex Task