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/backend/src/http/server.ts

@@ -4,6 +4,7 @@ import { initializeDatabase } from "../shared/database/index.js";
 import { createChildLogger } from "../shared/logger/index.js";
 import { createHttpApp } from "./app.js";
 import { createWebSocketServer } from "../ws/server.js";
+import { startRedisBridge } from "../ws/redis-bridge.js";
 
 const logger = createChildLogger("http.server");
 
@@ -18,6 +19,9 @@ export async function startHttpServer(): Promise<Server> {
   // Attach WebSocket server to the same HTTP server
   createWebSocketServer(server);
 
+  // Start Redis pub/sub bridge to forward discord-gateway events to WS clients
+  await startRedisBridge();
+
   return new Promise<Server>((resolve, reject) => {
     server.listen(port, () => {
       logger.info({ port }, "HTTP server started");