docs: unhide GraphQL API Reference page and add to overview

[devin-ai-integration]

Summary

Unhides the GraphQL API Reference page and adds it to the API references overview page.

Changes:

• Remove hidden: true from the GraphQL Reference entry in docs.yml
• Remove availability: pre-release frontmatter from the GraphQL page
• Remove the "not actively maintained" warning callout
• Add a GraphQL card to the API references overview page
• Link to both the live example site and GitHub source
• Apply matching changes to the Chinese translations

Review & Testing Checklist for Human

• Verify the GraphQL Reference page renders correctly at /learn/docs/api-references/generate-graphql-ref
• Verify the GraphQL card appears on the overview page at /learn/docs/api-references/overview
• Confirm the live example link works: https://graphql.docs.buildwithfern.com
• Confirm the GitHub source link works: https://github.com/fern-api/docs-examples/tree/main/graphql

Notes

Companion PR (merged): fern-api/docs-examples#10 — adds a plant-themed GraphQL example project to the docs-examples repo, now live at https://graphql.docs.buildwithfern.com

Link to Devin session: https://app.devin.ai/sessions/6ec297a50749439ab276ea17ccd914d7
Requested by: @devalog

[devin-ai-integration]

🤖 Devin AI Engineer

I'll be helping with this pull request! Here's what you should know:

✅ I will automatically:

• Address comments on this PR. Add '(aside)' to your comment to have me ignore it.
• Look at CI failures and help fix them

Note: I can only respond to comments from users who have write access to this repository.

⚙️ Control Options:

• Disable automatic comment and CI monitoring

[github-actions]

🌿 Preview your docs: https://fern-preview-devin-1779474024-unhide-graphql-ref.docs.buildwithfern.com/learn

Here are the markdown pages you've updated:

• learn/docs/api-references/generate-graphql-ref
• learn/docs/api-references/overview