feat: add Mattermost channel support

README.md

@@ -43,7 +43,7 @@
 | Install nanobot with no terminal/config background | [Start Without Technical Background](./docs/start-without-technical-background.md) |
 | Install quickly and get one CLI reply | [Install](#-install) and [Quick Start](#-quick-start) |
 | Open the bundled browser UI | [WebUI](#-webui) |
-| Connect Telegram, Discord, WeChat, Slack, Email, or another chat app | [Chat Apps](./docs/chat-apps.md) |
+| Connect Telegram, Discord, WeChat, Slack, Mattermost, Email, or another chat app | [Chat Apps](./docs/chat-apps.md) |
 | Configure providers, fallback models, Langfuse, MCP, web tools, or security | [Docs](./docs/README.md) and [Configuration](./docs/configuration.md) |
 | Understand or extend the internals | [Architecture](./docs/architecture.md) and [Development](./docs/development.md) |
 
@@ -205,7 +205,7 @@
 ## 💡 Why nanobot
 
 - **Persistent workflows**: goals, memory, tools, and chat context survive long-running work.
-- **Chat-native reach**: WebUI, API, Telegram, Feishu, Slack, Discord, Teams, and email.
+- **Chat-native reach**: WebUI, API, Telegram, Feishu, Slack, Mattermost, Discord, Teams, and email.
 - **Model freedom**: OpenAI-compatible APIs, local LLMs, image generation, search, and fallbacks.
 - **Small core**: readable internals with MCP, memory, deployment, and automation built in.
 - **Own your stack**: inspect, customize, self-host, and extend without a giant platform.