## Summary
- Add `PluginInstallPolicySource` to the app-server v2 `PluginSummary`
payload.
- Propagate remote `installation_policy_source` through plugin
summaries, details, installed-plugin caching, and app-server responses.
- Preserve the supported source values and map unrecognized backend
values to `null`.
- Return `null` for local plugins and expose the field in generated JSON
and TypeScript schemas.
- Update app-server API documentation and plugin list/read coverage.
## Testing
- `just test -p codex-app-server-protocol` (251 passed)
- Targeted `codex-app-server` plugin list, installed, and read tests (4
passed)
- Targeted `codex-core-plugins` known and unknown policy source tests (2
passed)
- `just fmt`
- `git diff --check`
c71895f63b