Add Pinchflat-style media manager: index channels into playlist folders

Index an entire YouTube channel or playlist once, then download it into
organized <Channel>/<Playlist>/<NNN> - <Title> folders, with incremental
re-sync. Built in six rebuild-gated phases (F-K); see ROADMAP-PINCHFLAT.md.

- F: channel-walk indexer (/playlists + /videos) -> persisted Source +
  MediaItem JSON stores; pure classify/dedup logic in indexerCore.ts
- G: Windows-safe folder paths + dir sanitizer (collectionOutputTemplate)
- H: Library tab + source tree + "Download pending" into the existing queue
- I: state-preserving re-index merge + persist-downloaded-on-complete
- J: watched sources, RSS fast-check, Task Scheduler + --sync launch
  (the OS-level scheduling/RSS need a real-install smoke test)
- K: .info.json / thumbnail / .description sidecars for media servers

Also gitignore .gitea-token. 106 unit tests pass; typecheck + build clean.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

ROADMAP.md

@@ -9,6 +9,11 @@ Sources: [Seal GitHub](https://github.com/JunkFood02/Seal) ·
 [Seal on F-Droid](https://f-droid.org/packages/com.junkfood.seal/) ·
 [It's FOSS overview](https://itsfoss.com/news/seal/).
 
+> **See also:** [ROADMAP-PINCHFLAT.md](ROADMAP-PINCHFLAT.md) — a parallel track that extends
+> AeroFetch from a one-shot downloader into a [Pinchflat](https://github.com/kieraneglin/pinchflat)-style
+> media manager (index entire channels → organize into `Channel / Playlist / Title` folders →
+> keep in sync), reusing the existing queue/history/options rather than replacing them.
+
 ---
 
 ## Already at parity ✅