feat(podcasts): #6 quick wins — tab badge, remember speed, sleep timer, persist queue

- Unread badge on the Podcasts tab via a new observable PodcastLibrary store
  that mirrors PodcastIndex; all played/remove/generation mutations route
  through it so the count stays live.
- Persist playback speed across sessions (UserDefaults), applied on setup.
- Sleep timer (15/30/45 min or end-of-episode) with a moon menu in the full
  player; end-of-episode stops instead of auto-advancing.
- Persist the current episode + Up Next queue and restore a *paused* session on
  launch; save position when backgrounding. Audio session is only claimed on
  actual playback so a restored session never interrupts other audio.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Marks/Services/PodcastGenerationManager.swift

@@ -66,6 +66,7 @@ final class PodcastGenerationManager {
                             title: status.title, parentBookmarkUrl: parentBookmarkUrl)
                         let finalTitle = status.title ?? title
                         finish(articleUrl)
+                        PodcastLibrary.shared.reload()   // new episode → refresh list + badge
                         Analytics.track("podcast.bg_completed", ["url": articleUrl])
                         onReady?(url, finalTitle)
                         return