Initial implementation of xtrm-agent multi-agent system

Multi-agent AI automation system with shared message bus, specialized
roles (coder/researcher/reviewer), and deny-by-default security.

- Config system with Pydantic validation and YAML loading
- Async message bus with inter-agent delegation
- LLM providers: Anthropic (Claude) and LiteLLM (DeepSeek/Kimi/MiniMax)
- Tool system: registry, builtins (file/bash/web), approval engine, MCP client
- Agent engine with tool-calling loop and orchestrator for multi-agent management
- CLI channel (REPL) and Discord channel
- Docker + Dockge deployment config
- Typer CLI: chat, serve, status, agents commands

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

xtrm_agent/channels/base.py

@@ -0,0 +1,22 @@
+"""Base channel interface."""
+
+from __future__ import annotations
+
+from abc import ABC, abstractmethod
+
+from xtrm_agent.bus import MessageBus
+
+
+class BaseChannel(ABC):
+    """Abstract base for all input/output channels."""
+
+    def __init__(self, bus: MessageBus) -> None:
+        self.bus = bus
+
+    @abstractmethod
+    async def start(self) -> None:
+        """Start listening for messages."""
+
+    @abstractmethod
+    async def stop(self) -> None:
+        """Clean up and stop."""