Add GET /api/v1/statistics/soundtracks with every soundtrack and its songs

The other soundtrack statistics are capped at 100, so a client that shows every soundtrack (the MusicPlayer statistics tab) had no way to get them all. This one has no limit and is sorted by name.

internal/server/statistics_handler.go

@@ -59,6 +59,11 @@ func (s *Server) registerStatistics(a apis) {
 	songs("get-least-played-songs", "/songs/least-played", "Least played songs",
 		"Returns the least played songs with their soundtrack.", st.LeastPlayedSongs)
 
+	register(s, a, op("get-all-soundtrack-statistics", "/soundtracks", "All soundtracks with statistics",
+		"Returns every soundtrack with its songs and play counts, sorted by name."),
+		func(ctx context.Context, _ *struct{}) (*jsonBody[[]backend.SoundtrackWithSongs], error) {
+			return ok(st.AllSoundtracks(ctx))
+		})
 	register(s, a, op("get-never-played-soundtracks", "/soundtracks/never-played", "Never played soundtracks",
 		"Returns all soundtracks that have never been played, with their songs."),
 		func(ctx context.Context, _ *struct{}) (*jsonBody[[]backend.SoundtrackWithSongs], error) {