Add Model Context Protocol integration documentation. (#36799)

* Add Model Context Protocol integration

* Update mcp documentation

* Tiny style tweaks

---------

Co-authored-by: c0ffeeca7 <38767475+c0ffeeca7@users.noreply.github.com>

source/_integrations/mcp.markdown

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+---
+title: Model Context Protocol
+description: Instructions on how to use the Model Context Protocol with Home Assistant.
+ha_category:
+  - Voice
+ha_release: 2025.2
+ha_iot_class: Local Polling
+ha_config_flow: true
+ha_codeowners:
+  - 'allenporter'
+ha_domain: mcp
+ha_integration_type: integration
+related:
+  - docs: /integrations/conversation/
+    title: Conversation
+---
+
+The [Model Context Protocol](https://modelcontextprotocol.io) is an open protocol that
+standardizes how applications provide context to LLMs. The **Model Context Protocol** {% term integration %}
+enables using MCP Servers in Home Assistant for providing additional tools to use with a
+[conversation agent](/integrations/conversation). For example, you can add an MCP server that
+supports memory functionality, or that can search the web using functionality not already
+available in Home Assistant.
+
+Controlling Home Assistant is done by providing MCP clients access to the Assist API of Home
+Assistant. You can control what devices and entities it can access from the {% my voice_assistants title="exposed entities page" %}.
+
+## Prerequisites
+
+1. You will need an [MCP server](https://modelcontextprotocol.io/examples).
+1. If your MCP server only supports the <abbr title="Standard input/output">*stdio*</abbr> protocol, you will also need an additional
+   MCP proxy (such as [mcp-proxy](https://github.com/sparfenyuk/mcp-proxy)) to expose
+   the server over <abbr title="Server-sent events">*SSE*</abbr>.
+
+{% include integrations/config_flow.md %}
+
+## Configuration options
+
+The integration provides the following configuration options:
+
+{% configuration_basic %}
+SSE Server URL:
+  description: The URL for the SSE endpoint of the MCP server. For example, `http://example/sse`.
+{% endconfiguration_basic %}
+
+## Architecture overview
+
+This {% term integration %} can provide additional functionality for LLM conversation agents
+(for example [Anthropic](/integrations/anthropic/), [Google Generative AI](/integrations/google_generative_ai_conversation), [Ollama](/integrations/ollama/), [Open AI](/integrations/openai_conversation/)). 
+
+Home Assistant acts as a client to the MCP server you specify. Home Assistant will
+poll the MCP server SSE endpoint and query the list of available tools. The tools are
+made available for use by Home Assistant conversation agents, similar to the Assist API.
+See the [Model Context Protocol Introduction](https://modelcontextprotocol.io/introduction#general-architecture)
+for more details on the protocol.
+
+The Home Assistant Model Context Protocol integration acts as a client using the
+[Server-Sent Events (SSE) transport](https://modelcontextprotocol.io/docs/concepts/transports#server-sent-events-sse)
+allowing streaming client-to-server communication. Most MCP clients today only support
+[stdio](https://modelcontextprotocol.io/docs/concepts/transports#standard-input-output-stdio) transport,
+and directly run an MCP server as a local command line tool. You can 
+use an MCP proxy server like [mcp-proxy](https://github.com/sparfenyuk/mcp-proxy)
+to enable Home Assistant to access an MCP SSE server.
+
+Once the integration is configured, you also need to configure the conversation
+agent to use the tools.
+
+## Supported functionality
+
+### Tools
+
+[MCP Tools](https://modelcontextprotocol.io/docs/concepts/tools) enable LLMs to
+perform actions through Home Assistant. The tools used by the configured LLM API
+are exposed.
+
+## Known limitations
+
+The Home Assistant Model Context Protocol integration currently only supports a
+subset of MCP features:
+
+| Feature | Supported by Home Assistant |
+| ------- | --------- |
+| Prompts | ❌ |
+| Tools | ✅ |
+| Resources | ❌ |
+| Sampling | ❌ |
+| Notifications | ❌ |
+
+## Troubleshooting
+
+See [Model Context Protocol: Debugging](https://modelcontextprotocol.io/docs/tools/debugging) for
+general tips on debugging MCP. If you are developing your own MCP server and having trouble making it work
+with Home Assistant, you can also use the [MCP Inspector](https://github.com/modelcontextprotocol/inspector)
+to verify that your MCP server is working correctly.
+
+
+## Remove integration
+
+This integration can be removed by following these steps:
+
+{% include integrations/remove_device_service.md %}