feat: implement all real backend endpoints, Redis pub/sub bridge, and gateway command handler

Backend (real implementations, no more stubs):
- Redis pub/sub bridge: subscribes to discord-gateway events (message/attachment/voice) and broadcasts to WS clients
- Redis command channel: backend publishes voice/media commands, discord-gateway executes and replies
- Voice service: connectVoice/disconnectVoice/getVoiceStatus via Redis commands with graceful fallback
- Media service: queue/skip/stop/volume via Redis commands, reads status from Redis cache
- Messages repository: ALL 7 methods now use real PostgreSQL queries (findMany, findById, findByChannel, create, update, delete, getAttachmentsByChannel)
- Analytics: period returns {start,end} epoch millis, overview includes hourly/topics/top_users, worst_flags as string[]
- Health check: actually queries SELECT 1 against database
- VoiceStatus type fixed: {connected, activeGuildId, activeChannelId, activeChannelName}
- Guild type: includes icon: string | null
- asyncHandler: accepts Promise<unknown> instead of Promise<void>

Discord Gateway:
- CommandHandler: subscribes to 'backend:command' Redis channel, executes voice/media commands, publishes replies
- Publishes voice:status and media:status to Redis for backend caching
- Shutdown handler updated to close command handler

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

services/discord-gateway/src/app/bootstrap.ts

@@ -1,5 +1,6 @@
 import { Client } from "discord.js-selfbot-v13";
 import { startPendingAIAnalysisWorker } from "../modules/ai-moderation/aiAnalyzer.js";
+import { CommandHandler } from "../modules/command-handler/commandHandler.js";
 import {
   EventBroadcaster,
   RedisEventPublisher,
@@ -43,12 +44,16 @@ export async function initializeDiscordGateway() {
   const redisPublisher = new RedisEventPublisher(config.REDIS_URL, logger);
   const eventBroadcaster = new EventBroadcaster(redisPublisher, logger);
 
+  // Initialize Redis command handler for backend→gateway commands
+  const commandHandler = new CommandHandler();
+
   const gracefulShutdown = createGracefulShutdown({
     logger,
     closeDatabase,
     voiceController,
     client,
     eventBroadcaster,
+    commandHandler,
   });
 
   try {
@@ -85,6 +90,10 @@ export async function initializeDiscordGateway() {
     setEventBroadcaster(eventBroadcaster);
     registerMessageCapture(client);
     startPendingAIAnalysisWorker(client);
+
+    // Start command handler after Discord is ready
+    commandHandler.start(client, voiceController);
+    logger.info("Command handler started");
   });
 
   client.on("error", (err) => {