Feature Request: Matrix channel plugin #26

Description

I'd love to see a Matrix channel plugin in addition to the existing Telegram plugin. The use case is simple: I want to chat with my JavaClaw agent via Matrix — either in a direct message or by inviting the bot into rooms/channels.

Why Matrix?

• Self-hostable & federated: Matrix fits perfectly with JavaClaw's privacy-first, self-hosted philosophy.
• Growing ecosystem: Matrix adoption is increasing, especially in privacy-conscious and enterprise environments (e.g., German public sector).
• Channel diversity: Adding Matrix alongside Telegram and the Chat UI would make JavaClaw significantly more versatile.

Voice support

The Telegram plugin doesn't seem to support voice messages yet, but if/when voice support lands in JavaClaw, it would be great to have it for Matrix as well. The project [baibot](https://github.com/etkecc/baibot) is an existing Matrix AI bot that already implements text chat, speech-to-text, text-to-speech, and E2EE in Matrix — it could serve as a useful reference for both the Matrix integration and voice capabilities.

Desired functionality

• Connect to a Matrix homeserver as a bot user
• Respond to direct messages
• Be invitable to Matrix rooms/channels to participate in conversations
• (Future) Voice message support (STT/TTS)