feat(music): persist live playback state to postgres

The queue and now-playing state only ever lived in the bot's memory,
so the dashboard had nothing real to show and a restart silently
wiped whatever was queued. Adds a musicrepo package and a syncState
call after every queue-changing action (play, skip, pause, volume,
stop, track end) that mirrors the current track and queue into
music_now_playing and music_queue.

No user-visible change yet, this is groundwork for the dashboard
queue/now-playing view.

internal/commands/music/public/play.go

@@ -64,7 +64,7 @@ func PlayHandler(s *discordgo.Session, i *discordgo.InteractionCreate) {
 		return
 	}
 
-	entry, started, err := music.EnqueueAndPlay(i.GuildID, vs.ChannelID, i.ChannelID, query, i.Member.User.Username)
+	entry, started, err := music.EnqueueAndPlay(i.GuildID, vs.ChannelID, i.ChannelID, query, i.Member.User.Username, i.Member.User.ID)
 	if err != nil {
 		_, _ = s.InteractionResponseEdit(i.Interaction, &discordgo.WebhookEdit{
 			Content: ptr(fmt.Sprintf("Error: %v", err)),