Document the OpenRemote MCP server

[Miggets7]

Problem

OpenRemote ships an MCP server (@openremote/mcp-server), which lets AI assistants query and manage an instance over the Model Context Protocol. The docs site has no page for it — the only mention is a single use-case bullet in the External Services page.

Proposal

Add a User Guide page covering:

• What the MCP server is and how it works (AI assistant → MCP server → REST API via a service user).
• Read vs write capabilities, described by category, deferring the full tool list to the npm page.
• Setup: create a service user + roles, Claude Desktop / Claude Code config, environment variables, Node 24+.
• Security caution: write roles let the model create/edit/delete data, and how to revoke access.
• Beta status and stdio-only transport.

Reference

• Package: https://www.npmjs.com/package/@openremote/mcp-server

Addressed by #176.