[Feature Request]Appspec.yml validation

There is a gap where the appspec.yml can be a valid yaml but incorrectly formatted which can cause the Ruby interpreter to crash.

An example is the permissions section:

```yaml
permissions:
- object: /tmp/my-app
pattern: "*-3.txt"
owner: adm
group: wheel
mode: 464
type:
- file
```

where type is expecting an array. If a str is given

```yaml
type: file
```

this will crash the agent with a message similar to the following:

```
put_host_command_complete(command_status:"Failed",diagnostics:{format:"JSON",payload:"{\"error_code\":5,\"script_name\":\"\",\"message\":\"undefined method `each' for \\\"file\\\":String\",\"log
```

首先定位 appspec.yml 的解析和权限处理，然后复现 issue 中描述的格式错误的 `type: file` 情况。完成标准是：格式不正确的值会被拒绝并给出明确的诊断，而不是导致 agent 崩溃。

由索引模型根据 Issue 内容生成。