Resolves the two deviations from the episode detail sheet:
- AI summary now shows in the detail sheet. Added a URL-keyed AISummaryStore
that BookmarksViewModel populates as it enriches/loads bookmarks, so the
decoupled Podcasts tab can surface a summary from just the episode URL —
without recoupling to BookmarksViewModel.
- "Open Bookmark" opens the in-app BrowserView as a nested sheet (generator
threaded through PodcastLibraryView / EpisodePickerView), alongside the
existing "Open in Safari" and Share.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>