feat: 增强 core/agents 工具和 API

- 新增 loop.py Agent 运行循环
- 优化 memory.py 记忆模块
- 扩展 api/routes.py 接口
- 更新 tools 模块：builtin.py, manager.py, __init__.py
- 新增 .env.example 配置示例
- 更新 requirements.txt 依赖

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

core/agents/requirements.txt

@@ -17,3 +17,7 @@ chromadb>=0.4.0
 
 # Utilities
 python-dotenv>=1.0.0
+
+# Sandbox isolation (optional)
+# Install gVisor for enhanced sandbox: https://gvisor.dev/
+# Or use bwrapfs which is available on most Linux systems