docs: document PAT auth and custom headers for Lightdash MCP (#699)

Clarifies that the MCP endpoint also accepts Personal Access Token and
service account auth alongside OAuth, and documents the X-Lightdash-Project
and X-Lightdash-User-Attributes headers used by headless agents.

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

Author: torimwhaley

references/integrations/lightdash-mcp.mdx

@@ -227,8 +227,10 @@ If you're building your own agents or automated workflows, you can integrate dir
 
 - **Transport**: Lightdash MCP exposes a StreamableHTTP transport endpoint at `https://<your_instance_name>.lightdash.cloud/api/v1/mcp`
 - **Debugging**: Use `@modelcontextprotocol/inspector` to inspect and debug the MCP connection
-- **Authentication**: Requires OAuth 2.0 flow for secure authentication
+- **Authentication**: For interactive setups use OAuth 2.0. For headless agents and automated workflows, you can authenticate with a Personal Access Token by passing `Authorization: ApiKey <token>` instead. Create the token under **Settings → Personal access tokens** for the user whose permissions and attributes you want the integration to use. Service account tokens are also supported on plans that include them.
 - **Documentation**: See the [MCP specification](https://modelcontextprotocol.io/docs) for implementation details
+- **Pin a project (optional)**: pass `X-Lightdash-Project: <project-uuid>` to scope the MCP session to a specific project, skipping the `set_project` step.
+- **Override user attributes per request (optional)**: pass `X-Lightdash-User-Attributes: <json>` to override the authenticated user's attributes for that request (useful for row-level security when an agent acts on behalf of different end-users).
 
 {/*<Accordion title="Example: Inspecting the MCP endpoint">