feat(music): consume playback commands via LISTEN/NOTIFY

The dashboard has been writing skip/pause/volume/etc. requests into
music_commands with nothing on this end reading them. Adds a
dedicated LISTEN connection (can't use the pooled *sql.DB for this,
LISTEN has to stay bound to one specific connection) that wakes on
NOTIFY, drains unprocessed rows, and dispatches each to the matching
Manager function. A command's error is logged, not fatal, and every
row gets marked processed regardless of outcome so a permanently
broken command doesn't retry forever.

main.go

@@ -73,7 +73,7 @@ func main() {
 	musicSettingsService := musicsettings.New(settingsRepo)
 	services := services.NewServices(levelService, levelSettingsService, meetingService, scheduleService, userSettingsService, projectsService, rpsService, twitchService, welcomeService, defaultRoleService, logSettingsService, musicSettingsService)
 
-	bot, err := bot.NewBot(config.BotToken, config.AppID, config.GuildID, config.LavalinkHost, config.LavalinkPass, commands.AllCommands, services, musicRepo)
+	bot, err := bot.NewBot(config.BotToken, config.AppID, config.GuildID, config.LavalinkHost, config.LavalinkPass, commands.AllCommands, services, musicRepo, config.DBHost)
 	if err != nil {
 		log.Fatalf("Error creating bot: %v", err)
 		return