feat: add conversation archive to daily cron

Add archiveOldConversations to the daily cron job (UTC 15:00 / KST 00:00).
Archives conversations older than 180 days by:
- Batching user messages into summaries (100 messages each)
- Using OpenAI to generate context-preserving summaries
- Deleting archived messages to reduce database size

Uses dynamic import for bundle size optimization and try-catch
to prevent errors from affecting other cron tasks.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/index.ts

@@ -277,10 +277,26 @@ export default {
       return;
     }
 
-    // 매일 자정 (KST): 입금 만료 + 정합성 검증
+    // 매일 자정 (KST): 입금 만료 + 정합성 검증 + 대화 아카이브
     if (cronSchedule === '0 15 * * *') {
       await cleanupExpiredDepositTransactions(env);
       await reconcileDepositBalances(env);
+
+      // 대화 아카이브 실행 (180일 이상 된 메시지)
+      try {
+        const { archiveOldConversations } = await import('./services/archive-service');
+        const result = await archiveOldConversations(env);
+        logger.info('대화 아카이브 완료', {
+          processedUsers: result.processed_users,
+          archivedMessages: result.archived_messages,
+          createdSummaries: result.created_summaries,
+          errorCount: result.errors.length,
+        });
+      } catch (error) {
+        logger.error('대화 아카이브 실패', error as Error);
+        // 에러가 다른 Cron 작업을 중단시키지 않도록 catch만 하고 계속 진행
+      }
+
       return;
     }