docs(mcp): restructure MCP docs and add OAuth 2.1 authorization (ENG-9125)

[asoorm]

Summary

• Restructure MCP docs from single 800-line page into multi-page architecture (overview, quickstart, operations, configuration, oauth, ide-setup)
• Add OAuth 2.1 authorization docs: 5-level scope enforcement, step-up authorization with WWW-Authenticate challenges, OR-of-AND scope semantics, RFC 9728 discovery
• Validate docs against router/pkg/mcpserver/ implementation and fix inaccuracies

Ported from wundergraph/cosmo-docs#260.

Test plan

• Preview deployment renders correctly
• Navigation group and internal links work
• OAuth section accurately reflects scope enforcement behavior

Summary by CodeRabbit

Documentation

• Restructured MCP Gateway documentation with expanded, dedicated guides
• Added quickstart guide for getting started with MCP integration
• New configuration reference with complete options table and environment variable mappings
• New guide for exposing GraphQL operations as AI model tools
• New OAuth 2.1 security and authentication documentation
• New setup guide for connecting IDE tools (Cursor, Claude Desktop, VS Code, Windsurf)

[coderabbitai]

Caution

Review failed

Pull request was closed or merged during review

Walkthrough

This PR reorganizes MCP Gateway documentation for Cosmo Router. It restructures the navigation in docs.json to create a dedicated MCP Gateway section with new subsections. The main MCP page is rewritten with a simplified overview, replacing detailed technical content. Five new documentation pages are added covering quickstart, operations authoring, configuration, OAuth security, and IDE setup.

Changes

Cohort / File(s)	Summary
Navigation Restructuring docs-website/docs.json	Reorganized MCP navigation structure by removing separate router/mcp group entry from router/configuration, creating a new MCP Gateway group with icon, and adding five new MCP subpages (quickstart, operations, configuration, oauth, ide-setup). Reintroduced Custom Modules group after MCP section.
Main MCP Overview docs-website/router/mcp.mdx	Substantially rewrote main MCP page with Cosmo Router–focused description. Removed top-level "AI Integration" section and replaced detailed technical content (tool naming, schema generation, full configuration reference, storage providers, installation guides) with simplified structure using CardGroups and navigation links. Updated frontmatter, support note specifying MCP spec 2025-06-18, and strengthened OAuth integration link.
New MCP Documentation Pages docs-website/router/mcp/quickstart.mdx, docs-website/router/mcp/configuration.mdx, docs-website/router/mcp/operations.mdx, docs-website/router/mcp/oauth.mdx, docs-website/router/mcp/ide-setup.mdx	Added five new pages providing: end-to-end quickstart setup flow, comprehensive configuration reference with options table and YAML examples, operations authoring guide with naming/validation rules, OAuth 2.1 security configuration with JWKS and scope enforcement details, and IDE/AI tool setup instructions with header forwarding behavior and tool-specific configurations (Cursor, Claude Desktop, Windsurf, VS Code).

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly describes the main change: restructuring MCP documentation and adding OAuth 2.1 authorization support. It is specific, concise, and accurately summarizes the primary objectives of this changeset.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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