feat: Add source_keyword-based article queries for dynamic outlet articles

- Add get_articles_by_source_keyword method to query articles by entities
- Search across entities.people, entities.organizations, and entities.groups
- Deprecate get_articles_by_ids method in favor of dynamic queries
- Support pagination for outlet article listings

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

services/news-api/backend/app/services/article_service.py

@@ -145,3 +145,71 @@ class ArticleService:
                 categories.append(doc["_id"])
 
         return categories
+
+    @staticmethod
+    async def get_articles_by_ids(language: str, article_ids: List[str]) -> List[Article]:
+        """여러 ID로 기사 조회 (Deprecated - use get_articles_by_source_keyword)"""
+        collection = get_collection(language)
+
+        if not article_ids:
+            return []
+
+        try:
+            # Convert string IDs to ObjectIds
+            object_ids = [ObjectId(aid) for aid in article_ids if ObjectId.is_valid(aid)]
+
+            cursor = collection.find({"_id": {"$in": object_ids}})
+
+            articles = []
+            async for doc in cursor:
+                doc["_id"] = str(doc["_id"])
+                articles.append(Article(**doc))
+
+            return articles
+        except Exception as e:
+            print(f"Error fetching articles by IDs: {e}")
+            return []
+
+    @staticmethod
+    async def get_articles_by_source_keyword(
+        language: str,
+        source_keyword: str,
+        page: int = 1,
+        page_size: int = 20
+    ) -> ArticleList:
+        """source_keyword로 기사 조회 (동적 쿼리) - entities 필드를 사용하여 검색"""
+        collection = get_collection(language)
+
+        # Query by source_keyword in multiple places:
+        # 1. Direct source_keyword field (for migrated articles)
+        # 2. entities.people, entities.organizations, entities.groups (for existing articles)
+        query = {
+            "$or": [
+                {"source_keyword": source_keyword},
+                {"entities.people": source_keyword},
+                {"entities.organizations": source_keyword},
+                {"entities.groups": source_keyword}
+            ]
+        }
+
+        # 전체 개수
+        total = await collection.count_documents(query)
+
+        # 페이지네이션
+        skip = (page - 1) * page_size
+        cursor = collection.find(query).sort("created_at", -1).skip(skip).limit(page_size)
+
+        articles = []
+        async for doc in cursor:
+            doc["_id"] = str(doc["_id"])
+            articles.append(Article(**doc))
+
+        total_pages = (total + page_size - 1) // page_size
+
+        return ArticleList(
+            total=total,
+            page=page,
+            page_size=page_size,
+            total_pages=total_pages,
+            articles=articles
+        )