feat(music): let the dashboard add songs, starting a session if needed

New AddToQueue appends to an already-active session without touching
voice (the dashboard can't join a channel on its own), and add_song's
dispatch case now branches: a voice_channel_id in the payload means
"start fresh", so it goes through EnqueueAndPlay (join + play) instead.
Query normalization (plain text -> YouTube search, stripping
autoplay/radio params off pasted YouTube URLs) moves out of /play's
handler into a shared NormalizeQuery, both entry points need it, not
just one.

Starting playback from the dashboard also posts the now-playing embed
into the voice channel's own built-in text chat, matching what /play
already does, instead of leaving it with nowhere to show up.

internal/commands/music/public/play.go

@@ -2,8 +2,6 @@ package public
 
 import (
 	"fmt"
-	"net/url"
-	"strings"
 	"velox-bot/internal/commands/music/shared"
 	"velox-bot/internal/music"
 
@@ -49,13 +47,6 @@ func PlayHandler(s *discordgo.Session, i *discordgo.InteractionCreate) {
 		return
 	}
 
-	// If user provided plain text, turn it into a YouTube search
-	if !strings.HasPrefix(query, "http://") && !strings.HasPrefix(query, "https://") && !strings.HasPrefix(query, "ytsearch:") {
-		query = "ytsearch:" + query
-	} else {
-		query = normalizeYouTubeRadioURL(query)
-	}
-
 	vs, err := findUserVoiceState(s, i.GuildID, i.Member.User.ID)
 	if err != nil {
 		_, _ = s.InteractionResponseEdit(i.Interaction, &discordgo.WebhookEdit{
@@ -90,37 +81,6 @@ func PlayHandler(s *discordgo.Session, i *discordgo.InteractionCreate) {
 
 func ptr[T any](v T) *T { return new(v) }
 
-// normalizeYouTubeRadioURL strips auto-generated "radio/mix" params like:
-// https://www.youtube.com/watch?v=ID&list=RDID&start_radio=1 -> https://www.youtube.com/watch?v=ID
-// It intentionally does NOT strip normal playlist URLs.
-func normalizeYouTubeRadioURL(raw string) string {
-	u, err := url.Parse(raw)
-	if err != nil || u == nil {
-		return raw
-	}
-
-	host := strings.ToLower(u.Host)
-	if !strings.Contains(host, "youtube.com") || u.Path != "/watch" {
-		return raw
-	}
-
-	q := u.Query()
-	v := q.Get("v")
-	if v == "" {
-		return raw
-	}
-
-	list := q.Get("list")
-	_, hasStartRadio := q["start_radio"]
-	if !hasStartRadio && !strings.HasPrefix(list, "RD") {
-		return raw
-	}
-
-	u.RawQuery = url.Values{"v": []string{v}}.Encode()
-	u.Fragment = ""
-	return u.String()
-}
-
 func findUserVoiceState(s *discordgo.Session, guildID, userID string) (*discordgo.VoiceState, error) {
 	g, err := s.State.Guild(guildID)
 	if err != nil {