feat(music): stable queue identity, remove/reorder, and repeat commands

TrackEntry gets a QueueID generated once when a track is queued and
kept for its whole life there, and musicrepo.ReplaceQueue now upserts
by that ID instead of deleting and reinserting the whole queue on
every sync (which churned every track's database id constantly, even
ones that hadn't moved, and would've made remove/reorder commands
target the wrong track). RemoveFromQueue and Reorder are new Manager
functions built on top of that stable identity. Also adds repeat_song/
repeat_queue to the persisted now-playing state, and makes the two
existing toggle functions actually sync it, they never did before.

go.mod

@@ -15,6 +15,7 @@ require (
 require (
 	github.com/disgoorg/json v1.2.0 // indirect
 	github.com/golang/freetype v0.0.0-20170609003504-e2365dfdc4a0 // indirect
+	github.com/google/uuid v1.6.0 // indirect
 	github.com/gorilla/websocket v1.5.3 // indirect
 	github.com/jackc/pgpassfile v1.0.0 // indirect
 	github.com/jackc/pgservicefile v0.0.0-20240606120523-5a60cdf6a761 // indirect