feat(digest): Phase 4 Global News Digest (cluster-level batch summarization)

7일 rolling window 뉴스를 country × topic 2-level로 묶어 매일 04:00 KST 배치 생성.
search 파이프라인 미사용. documents → clustering → cluster-level LLM summarization → digest.

핵심 결정:
- adaptive threshold (0.75/0.78/0.80) + EMA centroid (α=0.7) + time-decay (λ=ln(2)/3)
- min_articles=3, max_topics=10/country, top-5 MMR diversity, ai_summary[:300] truncate
- cluster-level LLM only, drop금지 fallback (topic_label="주요 뉴스 묶음" + top member ai_summary[:200])
- importance_score country별 0~1 normalize + raw_weight_sum 별도 보존, max(score, 0.01) floor
- per-call timeout 25s + pipeline hard cap 600s
- DELETE+INSERT idempotent (UNIQUE digest_date), AIClient._call_chat 직접 호출 (client.py 수정 없음)

신규:
- migrations/101_global_digests.sql (2테이블 정규화)
- app/models/digest.py (GlobalDigest + DigestTopic ORM)
- app/services/digest/{loader,clustering,selection,summarizer,pipeline}.py
- app/workers/digest_worker.py (PIPELINE_HARD_CAP + CLI 진입점)
- app/api/digest.py (/latest, ?date|country, /regenerate, inline Pydantic)
- app/prompts/digest_topic.txt (JSON-only + 절대 금지 블록)

main.py 4줄: import 2 + scheduler add_job 1 + include_router 1.
plan: ~/.claude/plans/quiet-herding-tome.md

app/main.py

@@ -8,6 +8,7 @@ from sqlalchemy import func, select, text
 
 from api.auth import router as auth_router
 from api.dashboard import router as dashboard_router
+from api.digest import router as digest_router
 from api.documents import router as documents_router
 from api.news import router as news_router
 from api.search import router as search_router
@@ -26,6 +27,7 @@ async def lifespan(app: FastAPI):
     from apscheduler.triggers.cron import CronTrigger
     from services.search.query_analyzer import prewarm_analyzer
     from workers.daily_digest import run as daily_digest_run
+    from workers.digest_worker import run as global_digest_run
     from workers.file_watcher import watch_inbox
     from workers.law_monitor import run as law_monitor_run
     from workers.mailplus_archive import run as mailplus_run
@@ -54,6 +56,7 @@ async def lifespan(app: FastAPI):
     scheduler.add_job(mailplus_run, CronTrigger(hour=7), id="mailplus_morning")
     scheduler.add_job(mailplus_run, CronTrigger(hour=18), id="mailplus_evening")
     scheduler.add_job(daily_digest_run, CronTrigger(hour=20), id="daily_digest")
+    scheduler.add_job(global_digest_run, CronTrigger(hour=4, minute=0), id="global_digest")
     scheduler.add_job(news_collector_run, "interval", hours=6, id="news_collector")
     scheduler.start()
 
@@ -88,6 +91,7 @@ app.include_router(search_router, prefix="/api/search", tags=["search"])
 
 app.include_router(dashboard_router, prefix="/api/dashboard", tags=["dashboard"])
 app.include_router(news_router, prefix="/api/news", tags=["news"])
+app.include_router(digest_router, prefix="/api/digest", tags=["digest"])
 
 # TODO: Phase 5에서 추가
 # app.include_router(tasks.router, prefix="/api/tasks", tags=["tasks"])