Add Cloudflare docs search tool

[mattzcarey]

Summary

• add a new docs MCP tool for searching Cloudflare Developer Documentation
• back the tool with the same AI Search AutoRAG index used by docs.mcp.cloudflare.com (docs-mcp-rag)
• use the same tool description as the current mcp-server-cloudflare docs AI Search tool
• return XML-style docs result blocks in normal text content, while exposing typed results via outputSchema / structuredContent
• register docs in both code mode and ?codemode=false
• add the AI binding to staging and production Worker environments
• document the new third code-mode tool

Notes

The current docs MCP server at docs.mcp.cloudflare.com reports serverInfo.name = docs-ai-search and version = 0.4.8; this mirrors that AI Search implementation rather than the older Vectorize path.

/mcp remains OAuth/API-token protected so clients still receive the normal auth challenge and login flow.

Tests

• npm run check
  • passes with existing lint warning for src/tests/cloudflare-test.d.ts triple-slash reference
• staging unauthenticated /mcp smoke test returns expected OAuth 401 challenge