## What changed
- Add nullable `installedAt` metadata to `PluginSummary` and its generated schemas, expressed as a Unix timestamp in seconds.
- Preserve the backend installation time for remote plugins across plugin list, installed, read, and share-list responses. Return `null` when the timestamp is unavailable, including for local or uninstalled plugins and older backend responses.
## Testing
- Cover timestamp conversion in the remote plugin list integration test and the field's serialization and backward-compatible default in protocol tests.
GitOrigin-RevId: 8a1640320adb298874e1074e9891d1017ad06937