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/music/listener.go

@@ -0,0 +1,106 @@
+package music
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"log"
+	"strconv"
+	"velox-bot/internal/db/repos/musicrepo"
+
+	"github.com/jackc/pgx/v5"
+)
+
+func StartCommandListener(ctx context.Context, connString string, repo *musicrepo.Repo) error {
+	conn, err := pgx.Connect(ctx, connString)
+	if err != nil {
+		return fmt.Errorf("connect: %w", err)
+	}
+	defer conn.Close(ctx)
+
+	_, err = conn.Exec(ctx, "LISTEN music_commands")
+	if err != nil {
+		return fmt.Errorf("exec: %w", err)
+	}
+
+	for {
+		_, err := conn.WaitForNotification(ctx)
+		if err != nil {
+			return fmt.Errorf("waitfornotification: %w", err)
+		}
+
+		processCommands(ctx, repo)
+	}
+}
+
+func processCommands(ctx context.Context, repo *musicrepo.Repo) {
+	cmds, err := repo.ListUnprocessedCommands(ctx)
+	if err != nil {
+		log.Printf("music: failed to list unprocessed commands: %v", err)
+		return
+	}
+
+	for _, cmd := range cmds {
+		if err := dispatchCommand(cmd); err != nil {
+			log.Printf("music: command %d (%s) for guild %d failed: %v", cmd.ID, cmd.CommandType, cmd.GuildID, err)
+		}
+
+		if err := repo.MarkCommandProcessed(ctx, cmd.ID); err != nil {
+			log.Printf("music: failed to mark command %d processed: %v", cmd.ID, err)
+		}
+	}
+}
+
+func dispatchCommand(cmd musicrepo.MusicCommand) error {
+	guildID := strconv.FormatInt(cmd.GuildID, 10)
+
+	switch cmd.CommandType {
+	case "skip":
+		return Skip(guildID)
+
+	case "pause":
+		return Pause(guildID, true)
+
+	case "resume":
+		return Pause(guildID, false)
+
+	case "set_volume":
+		var payload struct {
+			Volume int `json:"volume"`
+		}
+		if err := json.Unmarshal(cmd.Payload, &payload); err != nil {
+			return fmt.Errorf("unmarshal payload: %w", err)
+		}
+		return SetVolume(guildID, payload.Volume)
+
+	case "remove_track":
+		var payload struct {
+			QueueID string `json:"queue_id"`
+		}
+		if err := json.Unmarshal(cmd.Payload, &payload); err != nil {
+			return fmt.Errorf("unmarshal payload: %w", err)
+		}
+		return RemoveFromQueue(guildID, payload.QueueID)
+
+	case "reorder":
+		var payload struct {
+			QueueID  string `json:"queue_id"`
+			Position int    `json:"position"`
+		}
+		if err := json.Unmarshal(cmd.Payload, &payload); err != nil {
+			return fmt.Errorf("unmarshal payload: %w", err)
+		}
+		return Reorder(guildID, payload.QueueID, payload.Position)
+
+	case "repeat_song":
+		ToggleRepeatSong(guildID)
+		return nil
+
+	case "repeat_queue":
+		ToggleRepeatQueue(guildID)
+		return nil
+
+	default:
+		return fmt.Errorf("unknown command type %q", cmd.CommandType)
+	}
+}