Add link tools to MCP server

[theletterf]

This PR adds crosslink checking tools to the MCP server added in #2368

Changes

• src/Elastic.Documentation.Mcp/LinkTools.cs — Cross-link tools implementation.

Available tools

Tool	Description
ResolveCrossLink	Resolves a cross-link (like docs-content://get-started/intro.md) to its target URL and returns available anchors.
ListRepositories	Lists all repositories available in the cross-link index with their metadata.
GetRepositoryLinks	Gets all pages and their anchors published by a specific repository.
FindCrossLinks	Finds all cross-links between repositories. Can filter by source or target repository.
ValidateCrossLinks	Validates cross-links to a repository and reports any broken links.

Other changes

• Added ModelContextProtocol and Microsoft.Extensions.Hosting packages to Directory.Packages.props.
• Added new project to docs-builder.slnx.
• Added documentation at docs/mcp/index.md.

Testing locally in Cursor

1. Build the MCP project:

   dotnet build src/Elastic.Documentation.Mcp/Elastic.Documentation.Mcp.csproj

2. Create .cursor/mcp.json in your workspace (or globally in ~/.cursor/mcp.json):

   {
     "mcpServers": {
       "docs-builder": {
         "command": "dotnet",
         "args": [
           "run",
           "--project",
           "/path/to/docs-builder/src/Elastic.Documentation.Mcp/Elastic.Documentation.Mcp.csproj"
         ]
       }
     }
   }

3. Restart Cursor or reload the window.

4. Open Cursor chat in Agent mode and verify the tools are available. You should see ResolveCrossLink, ListRepositories, GetRepositoryLinks, FindCrossLinks, and ValidateCrossLinks in the tools list.

5. Test by asking the agent to use the tools:

   • "List all repositories in the cross-link index"
   • "Resolve the cross-link elasticsearch://reference/query-languages/querydsl.md"
   • "Find cross-links from docs-content to elasticsearch"
   • "Validate cross-links to the kibana repository"

[github-actions]

🔍 Preview links for changed docs

• docs/mcp/index.md

[theletterf]

@Mpdreamz @reakaleek Merged #2376 — seems to work pretty well!

[theletterf]

AOT compatible serializer works well!

[Mpdreamz]

One implementation feedback, not blocking I can follow up with that if unclear.