Turns the Podcasts tab into a proper podcast-app experience across three
features that compose on a shared background-generation service.
Background generation (#2)
- New PodcastGenerationManager runs generate→poll→download off the player,
so producing a new episode never stops current playback.
- Headphone taps never interrupt: idle → generate-and-play in the foreground
(unchanged); already playing → generate in the background, episode lands in
the library. A "Generating…" banner surfaces active jobs.
Played/unplayed + queue (#1)
- PodcastEntry gains playedAt (old index.json decodes as unplayed).
- Podcasts tab splits into Up Next / Played with a Play All queue that
auto-advances; finishing marks played; swipe to toggle played state.
Share-extension audio (#3)
- "Create podcast" toggle on the save card, plus configurable Auto-Podcast
Tags in Settings. The extension enqueues a request into the App Group; the
main app drains it on launch/foreground and generates in the background.
Closes#1Closes#2Closes#3
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
