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.
load plugin-apps from `.app.json`.
make apps runtime-mentionable iff `codex_apps` MCP actually exposes
tools for that `connector_id`.
if the app isn't available, it's filtered out of runtime connector set,
so no tools are added and no app-mentions resolve.
right now we don't have a clean cli-side error for an app not being
installed. can look at this after.
### Tests
Added tests, tested locally that using a plugin that bundles an app
picks up the app.
Update config.toml plugin entries to use
<plugin_name>@<marketplace_name> as the key.
Plugin now stays in
[plugins/cache/marketplace-name/plugin-name/$version/]
Clean up the plugin code structure.
Add plugin install functionality (not used yet).
xl-openai