feat: sync Playlists, wip: pair songs

BUGS.md

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+# Bugs
+
+- syncJukeboxIfToken() is always called at startup, even if we have a jukebox already
+
+- "Caveat: If a sync gets past the fetch phase, runs clearAllTables(), then dies while writing some playlists, you could still end up with a partial cache. Fixing that would mean a single Room transaction or a “swap” strategy; say if you want that next."
+
+- "playlists 401" in Playlists Activity should send us back to the Spotify auth screen
+
+- the server should implement some rate limiting / deadman switch / to avoid spamming Spotify API with broken-app API calls
+
+
+## Nice-to
+
+- TrackFileMatching, scoreAgainstLocalHints
+	- these are very rudimentary heuristics to pairing mp3 files to the playlists. check them again.
+
+- Playlist has empty name, id=0gjOliftUAwV48X6KK9EeP
+	- in our server-side api, we might want to log such events too
+.
+
+- (pairing songs) "Possible race: openTree callback may capture an empty tracks list if the folder was picked before LiveData emitted."
+
+
+- toast: "no tracks loaded for this playlist yet.  [...]"