feat: 新增 core/agents 模块和 nanobot

- 新增 agents 模块，包含 agent、api、skills 等子模块
- 新增 nanobot 项目，支持多渠道集成
- 添加启动脚本 start-all.bat 和 start-all.sh

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

core/agents/agent/__init__.py

@@ -0,0 +1,7 @@
+"""X-Agents Agent Module."""
+
+from agents.agent.loop import AgentLoop
+from agents.agent.context import ContextBuilder
+from agents.agent.memory import AgentMemory, SessionMemory, RemoteMemoryClient
+
+__all__ = ["AgentLoop", "ContextBuilder", "AgentMemory", "SessionMemory", "RemoteMemoryClient"]