v0.17.0: the desktop already knows what the songs are

The first half of andTunes, a music player for the Rabbit R1. Auxio re-reads
Android's MediaStore on every launch, which is the "your songs will show up
here" hang — so the answer isn't a faster scanner, it's not scanning at all.
LinTunes already knows the artist, album and year of every file it just
copied, so it writes them into Music/andTunes/library.json and the app reads
one file instead of indexing a filesystem.

New lintunes/andtunes/: layout.py (a de-duplicated Media/<Artist>/<Album>/
tree, so a song in three playlists is stored once), manifest.py (pure, Qt-free),
art.py (one 480 px cover per album via QImage, cached and invalidated by the
audio file's mtime — which is exactly what embedding new art moves), and
sync.py, a third sibling of plan_export/ExportWorker.

Three rules the code depends on: planning never renders art (a mutagen open
per album, and planning runs on the GUI thread); the index is written last and
after a cancel lists only tracks whose files actually landed; and every delete
goes through layout.assert_inside, which is why the old Music/<Playlist>/
folders are structurally unreachable rather than merely un-referenced.

Connections gains "Sync to Rabbit" and "Rabbit Sync Settings…" — the ticked
set is the device's contents, so unticking is how a playlist comes off, which
nothing could do before. The selection rides preferences.json so both machines
agree. The old per-playlist sync stays, renamed "(Auxio)": removing it now
would leave the device full of files and nothing able to open them until the
app exists.

The app itself is rounds 48-50; its board is andtunes/TASKS.md, including the
measured screen facts (480x640 px at density override 160 — one dp is half its
usual physical size on a 2.88" panel).

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015wrTys5U1fLb4pBD2LKWzV

lintunes/preferences.py

@@ -33,6 +33,14 @@ DEFAULTS = {
     "acoustid": {
         "api_key": "",
     },
+    # Which playlists belong on the andTunes device, by persistent_id. Kept
+    # here rather than on the Playlist so it stays out of the conflict-merge
+    # machinery — and because riding the syncthing share is the point: both
+    # machines should agree on what the Rabbit is carrying.
+    "device_sync": {
+        "playlist_ids": [],
+        "copy_art": True,
+    },
 }
 
 
@@ -89,6 +97,15 @@ class Preferences(QObject):
     def acoustid(self) -> dict:
         return self._data["acoustid"]
 
+    def update_device_sync(self, **fields):
+        self._data["device_sync"].update(fields)
+        self.save()
+        self.changed.emit()
+
+    @property
+    def device_sync(self) -> dict:
+        return self._data["device_sync"]
+
     def save(self):
         self._path.parent.mkdir(parents=True, exist_ok=True)
         tmp = self._path.with_suffix(".json.tmp")