feat: implement Phase 3 automation workers
- Add automation_state table for incremental sync (last UID, last check)
- Add law_monitor worker: 국가법령정보센터 API → NAS/DB/CalDAV VTODO
(LAW_OC 승인 대기 중, 코드 완성)
- Add mailplus_archive worker: IMAP(993) → .eml NAS save + DB + SMTP
notification (imaplib via asyncio.to_thread, timeout=30)
- Add daily_digest worker: PostgreSQL/pipeline stats → Markdown + SMTP
(documents, law changes, email, queue errors, inbox backlog)
- Add CalDAV VTODO helper and SMTP email helper to core/utils.py
- Wire 3 cron jobs in APScheduler (law@07:00, mail@07:00+18:00,
digest@20:00) with timezone=Asia/Seoul
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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