Compact HE-AAC audio saves: server lane with fdkaac, shrink saved songs from Saved videos

CLAUDE.md

@@ -128,8 +128,19 @@ JSON shapes mirror the Tauri Rust bridge exactly — don't change one side alone
 - **Broken**: `POST /api/media/:id/redownload` (now-playing ⚠ Broken button). When a
   client falls back from a cached copy (`/api/streams?nocache=1`) the server also
   re-validates its copy and refetches it if it fails — never trusts one device's error.
-- Ops: `curl https://worship.hesed.sbs/api/media/stats`; files under
-  `/app/data/media` in the container.
+- **Still-picture songs**: a fast still-check lane (keyframe scene scores, or 1 fps =
+  our own looped encode) marks `still=1`, writes `<id>.<gen>.jpg` + `audio_sha256`. Saves
+  send `?still=1` → the device stores `<id>.m4a` + OPFS `art/<id>.jpg` and plays it as
+  audio with the picture; online, still songs also play audio + `/api/media/:id/art`.
+- **Compact audio (HE-AAC)**: `<id>.<gen>.he.m4a`, ~48 kbps HE-AAC v1 from **fdkaac**
+  (Debian contrib — ffmpeg's encoder is LC only), one niced lane, made for every copy and
+  moved to the front when a device asks (`prepare?audio=he` → `working` until ready).
+  Columns `he_size` (NULL = not made, 0 = failed/not smaller) + `he_sha256`. Devices ask
+  for it with Settings → "Save songs as compact audio" or Saved videos → Shrink
+  (`shrinkSaved` swaps the file in place; `ytpCompactSaves` remembers which ones).
+  Saved `.m4a` files of YouTube ids are never offered to P2P (not the server's file).
+- Ops: `curl https://worship.hesed.sbs/api/media/stats` (`compactAudio`, `compactQueued`); files under
+  `$MEDIA_DIR` (`/app/bulk/media` on prod) in the container.
 
 ## Lyrics · chapters · bookmarks (`server/notes.js`, `frontend/lyrics-core.js`)
 - **Shared per video** (every user sees the same copy): `video_notes` holds the live