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/modules/mascot-chat/mascot-chat.service.ts

@@ -15,6 +15,10 @@ class MascotChatService {
     context: MascotChatContext | undefined,
     userId: string,
   ): Promise<string> {
+    logger.info(
+      { userId, messageLength: message.length },
+      "processMessage called",
+    );
     const recentContext = await this.getRecentConversationContext(userId);
     const serverInsights = await mascotChatRepository.getServerInsights(
       context?.guildId,
@@ -34,6 +38,7 @@ class MascotChatService {
   }
 
   async saveConversation(input: SaveConversationInput): Promise<void> {
+    logger.info({ userId: input.userId }, "saveConversation called");
     await mascotChatRepository.saveConversation(input);
   }
 
@@ -41,10 +46,12 @@ class MascotChatService {
     userId: string,
     limit: number,
   ): Promise<MascotChatHistoryRow[]> {
+    logger.debug({ userId, limit }, "getChatHistory called");
     return mascotChatRepository.getChatHistory(userId, limit);
   }
 
   async clearChatHistory(userId: string): Promise<void> {
+    logger.info({ userId }, "clearChatHistory called");
     await mascotChatRepository.clearChatHistory(userId);
   }