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/modules/ai-moderation/autoDeleteNotify.ts

@@ -0,0 +1,46 @@
+import { createChildLogger } from "@bete/shared/logger";
+import type { Client } from "discord.js-selfbot-v13";
+import { config } from "../../shared/config/config.js";
+import type { MessageRecord } from "../message-capture/types.js";
+
+const logger = createChildLogger("auto-delete-notify");
+
+/**
+ * Send a DM notification to the user whose message was auto-deleted.
+ * If AUTO_DELETE_NOTIFY_USER is disabled, this is a no-op.
+ * DM failures (user has DMs disabled, etc.) are logged at debug level and swallowed.
+ */
+export async function sendDeletionNotification(
+  client: Client,
+  message: MessageRecord,
+  guildName: string,
+): Promise<void> {
+  if (!config.AUTO_DELETE_NOTIFY_USER) return;
+
+  try {
+    const targetUser = await client.users.fetch(message.user_id);
+    if (targetUser) {
+      const reason: string =
+        message.ai_categories ?? message.ai_moderation_flags ?? "(unknown)";
+      await targetUser.send(
+        `Pesan Anda di **${guildName}** telah dihapus oleh sistem moderasi otomatis.\n` +
+          `Alasan: ${reason}\n` +
+          `Jika Anda merasa ini adalah kesalahan, silakan hubungi admin server.`,
+      );
+      logger.info(
+        { userId: message.user_id, messageId: message.id },
+        "Deletion notification sent",
+      );
+    }
+  } catch (dmErr) {
+    // DM might fail if user has DMs disabled — not critical
+    logger.debug(
+      {
+        messageId: message.id,
+        userId: message.user_id,
+        error: String(dmErr),
+      },
+      "Failed to send DM notification for auto-deleted message",
+    );
+  }
+}