Streamable HTTP MCP endpoint.

Put this after Plug.Parsers in the host endpoint so it runs before the browser pipeline (CSRF / accepts: html):

plug Plug.Parsers, parsers: [:urlencoded, :multipart, :json], pass: ["*/*"], json_decoder: Jason
plug PhoenixLensWeb.Plugs.MCP, path: "/lens/mcp"

Authenticate with Authorization: Bearer <secret> from Settings → MCP.