refactor: atomic, DRY, and logging improvements

- Shared Redis channel constants as single source of truth (redis-channels.ts)
- commandHandler.ts split into VoiceHandler, MediaHandler, GuildHandler,
  ModerationHandler with handler-registry.ts dispatch
- messageStore.ts (1322 lines) split into domain-specific DB files:
  messages.db.ts, attachments.db.ts, reviews.db.ts,
  moderation-actions.db.ts, retention.db.ts
- recorder.ts startSpeaking callback extracted into speakingHandler.ts,
  streamSetup.ts, segmentFinalizer.ts
- autoDeleteManager.ts split into autoDeleteEligibility.ts,
  autoDeleteNotify.ts, autoDeleteLogger.ts
- Added createChildLogger() logging across 8 service files
- Backend messages.repository.ts migrated from raw SQL to Drizzle ORM
- Fixed biome.json to exclude packages/**/dist/* from lint
- Fixed config.ts GUILD_ID pre-existing type error

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

services/backend/src/ws/server.ts

@@ -1,4 +1,5 @@
 import type { Server } from "node:http";
+import { BACKEND_COMMAND, BACKEND_VOICE_TRANSMIT } from "@bete/shared";
 import { createChildLogger } from "@bete/shared/logger";
 import { WebSocket, WebSocketServer } from "ws";
 import { setBroadcastFunctions } from "./broadcast.js";
@@ -92,7 +93,7 @@ export function createWebSocketServer(server: Server): WebSocketServer {
                 const publisher = getCommandPublisher();
                 publisher
                   .publish(
-                    "backend:voice:transmit",
+                    BACKEND_VOICE_TRANSMIT,
                     JSON.stringify({
                       type: "pcm",
                       buffer: message.buffer,
@@ -114,7 +115,7 @@ export function createWebSocketServer(server: Server): WebSocketServer {
                 const commandId = `cmd-${Date.now()}-${Math.random().toString(36).slice(2, 9)}`;
                 publisher
                   .publish(
-                    "backend:command",
+                    BACKEND_COMMAND,
                     JSON.stringify({
                       id: commandId,
                       type: message.command,