docs: Add GitHib copilot instruction files

[marcel-rbro]

Note

Adds .github/copilot-instructions.md detailing repo-specific context and writing guidelines for AI tools (OpenAPI pipeline, theme, patterns, QA, and style).

• Docs:
  • New AI agent guide in .github/copilot-instructions.md providing:
    • Project overview & architecture: Docusaurus multi-repo setup, custom theme workspace.
    • OpenAPI build pipeline: source locations, Redocly plugins, build command, generated outputs.
    • Project patterns: OpenAPI code samples, slug collection, external link processing, LLMs.txt generation.
    • Quality & pitfalls: broken links, frontmatter, code block languages; local build, linting, OpenAPI validation.
    • Quick reference for common tasks and navigation updates.
    • Writing & style guidelines: frontmatter schema, naming, formatting, admonitions, terminology.
    • Content review checklist and doc type guidelines; related references (CONTRIBUTING.md, AGENTS.md).

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[apify-service-account]

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[apify-service-account]

Preview for this PR was built for commit d48f9845 and is ready at https://pr-2146.preview.docs.apify.com!