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.

internal/bot/bot.go

@@ -1,6 +1,7 @@
 package bot
 
 import (
+	"context"
 	"log"
 	"velox-bot/internal/commands"
 	"velox-bot/internal/db/repos/musicrepo"
@@ -19,11 +20,12 @@ type Bot struct {
 	registeredCommands []*discordgo.ApplicationCommand
 	Services           *services.Services
 	MusicRepo          *musicrepo.Repo
+	DBHost             string
 	LavalinkHost       string
 	LavalinkPass       string
 }
 
-func NewBot(token, appID, guildID, lavalinkHost, lavalinkPass string, cmds []*discordgo.ApplicationCommand, services *services.Services, musicRepo *musicrepo.Repo) (*Bot, error) {
+func NewBot(token, appID, guildID, lavalinkHost, lavalinkPass string, cmds []*discordgo.ApplicationCommand, services *services.Services, musicRepo *musicrepo.Repo, dbHost string) (*Bot, error) {
 	session, err := discordgo.New("Bot " + token)
 	if err != nil {
 		return nil, err
@@ -49,6 +51,7 @@ func NewBot(token, appID, guildID, lavalinkHost, lavalinkPass string, cmds []*di
 		Commands:     cmds,
 		Services:     services,
 		MusicRepo:    musicRepo,
+		DBHost:       dbHost,
 		LavalinkHost: lavalinkHost,
 		LavalinkPass: lavalinkPass,
 	}, nil
@@ -61,6 +64,12 @@ func (b *Bot) Start() error {
 
 	_ = music.Init(b.Session, b.MusicRepo, b.AppID, b.LavalinkHost, b.LavalinkPass)
 
+	go func() {
+		if err := music.StartCommandListener(context.Background(), b.DBHost, b.MusicRepo); err != nil {
+			log.Printf("music: command listener stopped: %v", err)
+		}
+	}()
+
 	b.registeredCommands = make([]*discordgo.ApplicationCommand, len(b.Commands))
 	for _, cmd := range b.Commands {
 		created, err := b.Session.ApplicationCommandCreate(b.AppID, b.GuildID, cmd)