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/discord-gateway/src/shared/config/config.ts

@@ -13,7 +13,7 @@ export function loadConfig(env: NodeJS.ProcessEnv = process.env): AppConfig {
   return {
     ...parsed,
     EFFECTIVE_TEXT_GUILD_ID: parsed.TEXT_GUILD_ID ?? parsed.MONITOR_GUILD_ID,
-    EFFECTIVE_VOICE_GUILD_ID: parsed.VOICE_GUILD_ID ?? parsed.GUILD_ID,
+    EFFECTIVE_VOICE_GUILD_ID: parsed.VOICE_GUILD_ID,
   };
 }