#### What
on `plugin/install`, check if installed apps are already authed on
chatgpt, and return list of all apps that are not. clients can use this
list to trigger auth workflows as needed.
checks are best effort based on `codex_apps` loading, much like
`app/list`.
#### Tests
Added integration tests, tested locally.
Support marketplace.json that points to a local file, with
```
"source":
{
"source": "local",
"path": "./plugin-1"
},
```
Add a new plugin/install endpoint which add the plugin to the cache folder and enable it in config.toml.
