feat: implement researcher and publication management with sync functionality

backend/app/repositories/researcher_repository.py

@@ -0,0 +1,25 @@
+from sqlalchemy.orm import Session
+from app.db.models import Researcher
+from sqlalchemy.sql import func
+
+
+class ResearcherRepository:
+
+    @staticmethod
+    def get_by_orcid(db: Session, orcid_id: str):
+        return db.query(Researcher).filter(Researcher.orcid_id == orcid_id).first()
+
+    @staticmethod
+    def create(db: Session, orcid_id: str, name: str = None):
+        researcher = Researcher(orcid_id=orcid_id, name=name)
+        db.add(researcher)
+        db.commit()
+        db.refresh(researcher)
+        return researcher
+
+    @staticmethod
+    def update_last_sync(db: Session, researcher: Researcher):
+        researcher.last_sync_at = func.now()
+        db.commit()
+        db.refresh(researcher)
+        return researcher