Add frontend storage and restore flow for active backend downloads so
workflow context, missing model bindings, and queue UI state survive
browser refreshes.
- Add queue storage methods for loading/saving/removing active download
recovery entries with serializable metadata.
- Add restoreActiveDownloadsFromBackend and rebindActiveDownloadMissingModels
to resolve_download_methods.
- Hook restore and rebind into lifecycle graph methods.
- Add tests for recovery persistence and refresh restoration behavior.
Dariusz L