fix(voice): resolve Redis subscriber corruption, transmitter races, and DB error logging

Redis root cause: VoiceHandler passed redisPub to transmitter.start(),
which called .subscribe() on it — permanently converting the publish
connection to subscriber mode. Every subsequent command reply and status
update failed.

Fixes:
1. Transmitter now creates its own Redis client via new IORedis()
2. Mutual exclusion gate serialises start/stop to prevent null-deref races
3. PassThrough drain listeners cleaned up to stop MaxListenersExceeded
4. FFmpeg SIGTERM flagged as expected exit (no more false level-50 errors)
5. Voice recording repo captures PG error code/detail for diagnostics

Co-Authored-By: Claude <noreply@anthropic.com>

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

@@ -81,7 +81,6 @@ export class CommandHandler {
     this.voiceHandler = new VoiceHandler(
       client,
       voiceController,
-      this.redisPub,
     );
     this.mediaHandler = new MediaHandler();
     this.guildHandler = new GuildHandler(client);

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

@@ -5,7 +5,6 @@ import {
 } from "@bete/shared";
 import { createChildLogger } from "@bete/shared/logger";
 import type { Client } from "discord.js-selfbot-v13";
-import type Redis from "ioredis";
 import { config } from "../../shared/config/config.js";
 import { discordPlayer } from "../voice-recording/player.js";
 import { voiceTransmitter } from "../voice-recording/transmitter.js";
@@ -21,7 +20,6 @@ export class VoiceHandler {
   constructor(
     private client: Client | null,
     private voiceController: VoiceController | null,
-    private sharedRedis: Redis | null = null,
   ) {}
 
   setClient(client: Client): void {