feat(digest): date picker URL sync + article→문서 라우팅 + country 국기·한국어

- GET /api/digest/dates 신설 (브리핑 /briefing/dates 패턴 미러, read-only)
- topic article 제목 enrich (documents 배치 1쿼리 + dedupe(set) + map-miss=null → 프론트 '(제목 없음)')
- /digest 재작성: ?date=&country= URL sync(공유·뒤로가기), 국가 탭=인라인 SVG 국기+한국어, 기사=/documents/{id} 링크(상위5+펼치기)
- Phase 4.5(PR #22) 후속. 검증: py_compile·dates/enrich 쿼리(275 resolve·miss 0)·frontend docker build PASS. 시각 렌더 검증=preview 게이트 대기

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/api/digest.py

@@ -2,11 +2,15 @@
 
 엔드포인트:
 - GET  /api/digest/latest                 : 가장 최근 digest
+- GET  /api/digest/dates                  : 생성된 digest 날짜 목록 (date picker 용)
 - GET  /api/digest?date=YYYY-MM-DD         : 특정 날짜 digest
 - GET  /api/digest?country=KR              : 특정 국가만
 - POST /api/digest/regenerate              : 백그라운드 digest 워커 트리거 (auth 필요)
 
 응답은 country → topic 2-level 구조. country 가 비어있는 경우 응답에서 자동 생략.
+각 topic 은 article_ids(doc_id) 와 함께 articles([{id, title}]) 를 반환 — title 은 documents
+배치 조회로 채우며(한 digest 당 1 쿼리), 매칭 없는 id(하드삭제 등)는 title=null 로 둔다
+(프론트는 "(제목 없음)" 으로 렌더, 빈 링크 금지). article → /documents/{id} 라우팅용.
 """
 
 import asyncio
@@ -23,6 +27,7 @@ from sqlalchemy.orm import selectinload
 from core.auth import get_current_user, require_admin
 from core.database import get_session
 from models.digest import DigestTopic, GlobalDigest
+from models.document import Document
 from models.user import User
 
 router = APIRouter()
@@ -31,11 +36,17 @@ router = APIRouter()
 # ─── Pydantic 응답 모델 (schemas/ 디렉토리 미사용 → inline 정의) ───
 
 
+class ArticleRef(BaseModel):
+    id: int
+    title: str | None = None
+
+
 class TopicResponse(BaseModel):
     topic_rank: int
     topic_label: str
     summary: str
     article_ids: list[int]
+    articles: list[ArticleRef]
     article_count: int
     importance_score: float
     raw_weight_sum: float
@@ -62,21 +73,65 @@ class DigestResponse(BaseModel):
     countries: list[CountryGroup]
 
 
+class DigestDateSummary(BaseModel):
+    """date picker 용 경량 요약 (브리핑 /briefing/dates 와 동형)."""
+
+    digest_date: date_type
+    total_topics: int
+    total_countries: int
+    total_articles: int
+    status: str
+
+
 # ─── helpers ───
 
 
-def _build_response(digest: GlobalDigest, country_filter: str | None = None) -> DigestResponse:
-    """ORM 객체 → DigestResponse. country_filter 가 주어지면 해당 국가만."""
+def _collect_article_ids(digest: GlobalDigest) -> set[int]:
+    """digest 의 모든 topic article_ids 를 dedupe 한 set (배치 title 조회용).
+
+    같은 기사가 여러 topic 에 걸리면 중복 id 가 생기므로 set 으로 한 번 줄인다.
+    """
+    ids: set[int] = set()
+    for t in digest.topics:
+        for aid in t.article_ids or []:
+            try:
+                ids.add(int(aid))
+            except (TypeError, ValueError):
+                continue
+    return ids
+
+
+async def _fetch_titles(session: AsyncSession, ids: set[int]) -> dict[int, str | None]:
+    """doc_id → title 배치 조회. 매칭 없는 id 는 map 에 부재(호출부가 None 처리)."""
+    if not ids:
+        return {}
+    result = await session.execute(
+        select(Document.id, Document.title).where(Document.id.in_(ids))
+    )
+    return {row.id: row.title for row in result.all()}
+
+
+def _build_response(
+    digest: GlobalDigest,
+    title_map: dict[int, str | None],
+    country_filter: str | None = None,
+) -> DigestResponse:
+    """ORM 객체 → DigestResponse. country_filter 가 주어지면 해당 국가만.
+
+    title_map miss(삭제/아카이브된 문서)는 title=None 으로 — 프론트가 "(제목 없음)" 처리.
+    """
     topics_by_country: dict[str, list[TopicResponse]] = {}
     for t in sorted(digest.topics, key=lambda x: (x.country, x.topic_rank)):
         if country_filter and t.country != country_filter:
             continue
+        ids = [int(a) for a in (t.article_ids or [])]
         topics_by_country.setdefault(t.country, []).append(
             TopicResponse(
                 topic_rank=t.topic_rank,
                 topic_label=t.topic_label,
                 summary=t.summary,
-                article_ids=list(t.article_ids or []),
+                article_ids=ids,
+                articles=[ArticleRef(id=aid, title=title_map.get(aid)) for aid in ids],
                 article_count=t.article_count,
                 importance_score=t.importance_score,
                 raw_weight_sum=t.raw_weight_sum,
@@ -120,6 +175,12 @@ async def _load_digest(
     return result.scalar_one_or_none()
 
 
+async def _respond(session: AsyncSession, digest: GlobalDigest, country_filter: str | None = None) -> DigestResponse:
+    """digest 1건 → article 제목 배치 enrich 후 응답 빌드."""
+    title_map = await _fetch_titles(session, _collect_article_ids(digest))
+    return _build_response(digest, title_map, country_filter=country_filter)
+
+
 # ─── Routes ───
 
 
@@ -132,7 +193,32 @@ async def get_latest(
     digest = await _load_digest(session, target_date=None)
     if digest is None:
         raise HTTPException(status_code=404, detail="아직 생성된 digest 없음")
-    return _build_response(digest)
+    return await _respond(session, digest)
+
+
+@router.get("/dates", response_model=list[DigestDateSummary])
+async def list_dates(
+    user: Annotated[User, Depends(get_current_user)],
+    session: Annotated[AsyncSession, Depends(get_session)],
+    limit: int = Query(default=60, ge=1, le=365, description="최신부터 N개"),
+):
+    """생성된 digest 날짜 목록 (date picker 용, 최신 내림차순)."""
+    query = (
+        select(GlobalDigest)
+        .order_by(GlobalDigest.digest_date.desc())
+        .limit(limit)
+    )
+    rows = (await session.execute(query)).scalars().all()
+    return [
+        DigestDateSummary(
+            digest_date=g.digest_date,
+            total_topics=g.total_topics,
+            total_countries=g.total_countries,
+            total_articles=g.total_articles,
+            status=g.status,
+        )
+        for g in rows
+    ]
 
 
 @router.get("", response_model=DigestResponse)
@@ -150,7 +236,7 @@ async def get_digest(
             detail=f"digest 없음 (date={date})" if date else "아직 생성된 digest 없음",
         )
     country_filter = country.upper() if country else None
-    return _build_response(digest, country_filter=country_filter)
+    return await _respond(session, digest, country_filter=country_filter)
 
 
 @router.post("/regenerate")