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/shell_executor/__init__.py

@@ -29,6 +29,16 @@ async def shell_executor(command: str, timeout: int = 30) -> str:
     Returns:
         命令的 stdout + stderr 输出
     """
+    from kilostar.utils.sandbox import (
+        validate_shell_command, CommandViolation, get_shell_timeout,
+    )
+
+    try:
+        command = validate_shell_command(command)
+    except CommandViolation as e:
+        return f"[Sandbox] {e}"
+    timeout = get_shell_timeout(timeout)
+
     try:
         proc = await asyncio.create_subprocess_shell(
             command,