Bug: plugin-config 停用分组后 操作分组内的插件 会报错

复现方式
1. 新建分组
2. 分组内添加插件
3. 停用分组
4. 启用或停用分组内的插件

错误日志
```
loader TypeError: Cannot read properties of undefined (reading 'ctx')
at Proxy.unload (/home/project/TSWorkSpace/koishi/development/koishi-dev/node_modules/@koishijs/plugin-config/src/shared/writer.ts:153:30)
at _Client.ctx.console.addListener.authority (/home/project/TSWorkSpace/koishi/development/koishi-dev/node_modules/@koishijs/plugin-config/src/shared/writer.ts:59:27)
at WebSocket.receive (/home/project/TSWorkSpace/koishi/development/koishi-dev/node_modules/@koishijs/plugin-console/node_modules/@koishijs/console/src/client.ts:35:45)
at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
```

分组停用后 应该禁止操作分组内的插件 只允许修改配置

Start by reading @koishijs/plugin-config/src/shared/writer.ts, especially the unload path around lines 153 and 59 shown in the stack trace. Reproduce the sequence of creating a group, adding a plugin, disabling the group, and toggling the plugin. Done means plugin operations are blocked while the group is disabled, while configuration changes remain allowed.

Written by the indexing model from the issue text.