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/.env.example

@@ -25,3 +25,10 @@ WORKSPACE=./workspace
 # Agent settings
 MAX_ITERATIONS=10
 TEMPERATURE=0.7
+
+# Sandbox Configuration (optional)
+# Enable sandbox mode for secure code execution (bwrap/gvisor)
+# SANDBOX_TYPE=bwrap  # Options: bwrap, gvisor, none
+# SANDBOX_TIMEOUT=60  # Default timeout in seconds
+# GVISCOR_RUNSC_PATH=runsc  # Path to gVisor runsc binary
+# BWRAP_PATH=bwrap  # Path to bwrap binary