wire plugin marketplace metadata through app-server endpoints:
- `plugin/list` has `installPolicy` and `authPolicy`
- `plugin/install` has plugin-level `authPolicy`
`plugin/install` also now enforces `NOT_AVAILABLE` `installPolicy` when
installing.
added tests.
1. Add a synced curated plugin marketplace and include it in marketplace
discovery.
2. Expose optional plugin.json interface metadata in plugin/list
3. Tighten plugin and marketplace path handling using validated absolute
paths.
4. Let manifests override skill, MCP, and app config paths.
5. Restrict plugin enablement/config loading to the user config layer so
plugin enablement is at global level
#### 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.
