feat(security): 新增工具沙箱安全机制

为所有工具插件添加沙箱拦截层，防止危险的文件访问、Shell命令和Python代码执行。
包含配置文件、核心校验逻辑及31个单元测试。

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

kilostar/plugin/tool_plugin/python_executor/__init__.py

@@ -32,6 +32,16 @@ async def python_executor(code: str, timeout: int = 30) -> str:
     Returns:
         代码的标准输出 + 标准错误
     """
+    from kilostar.utils.sandbox import (
+        validate_python_code, CodeViolation, get_python_timeout,
+    )
+
+    try:
+        code = validate_python_code(code)
+    except CodeViolation as e:
+        return f"[Sandbox] {e}"
+    timeout = get_python_timeout(timeout)
+
     tmp_file = None
     try:
         with tempfile.NamedTemporaryFile(