fix(voice): media queue field mismatch, voice joinable filter, connect error toast

Audit voice (kirim/terima/music/screenshare) menemukan 3 masalah:
1. media:queue SILENT no-op — backend publish {source,mode} tapi gateway
   handler baca payload.url → selalu 'received without a URL'. Backend
   sekarang kirim {url,mode}, gateway terima url ATAU source (robust).
2. Voice connect gagal diam-diam saat user pilih channel tanpa permission
   (joinable=false, contoh Music 32/64/128/256k). Backend+gateway sekarang
   expose joinable; FE disable channel 'no akses' + empty state.
3. FE tidak kasih feedback saat connect gagal — tambah toast.error dengan
   pesan dari backend.

Verified live: @discordjs/voice connect ke Lofi Radio joinable sukses
(VOICE READY, DAVE session OK) — pipeline voice sebenarnya sehat, masalah
utama UX. media:queue fix akan di-verify setelah deploy.

services/discord-gateway/src/modules/command-handler/media.handler.ts

@@ -124,7 +124,8 @@ export class MediaHandler {
   }
 
   async handleMediaQueue(cmd: CommandMessage): Promise<CommandReply<unknown>> {
-    const url = String(cmd.payload.url ?? "").trim();
+    // Accept both `url` (canonical) and `source` (legacy FE) for resilience.
+    const url = String(cmd.payload.url ?? cmd.payload.source ?? "").trim();
     const mode: MediaMode = cmd.payload.mode === "screen" ? "screen" : "music";
     const requestedBy = String(cmd.payload.requestedBy ?? "unknown");
 

services/discord-gateway/src/modules/command-handler/voice.handler.ts

@@ -128,6 +128,9 @@ export class VoiceHandler {
           id: c.id,
           name: c.name,
           type: "voice" as const,
+          // selfbot exposes joinable (permission check) — let FE filter
+          // channels the account actually may join.
+          joinable: (c as { joinable?: boolean }).joinable ?? true,
         }));
 
       return { id: cmd.id, success: true, data: voiceChannels };