feat: enhance backend security and configuration

- Updated Dockerfile to improve security with a non-root user and added health checks.
- Modified docker-compose.yml to set containers as read-only, restrict ports to localhost, and implement health checks.
- Enhanced .env.example with additional environment variables for security and configuration.
- Improved FastAPI application with middleware for security headers, CORS, and body size limits.
- Refactored authentication flow in auth.py to include state validation and improved error handling.
- Added rate limiting to various endpoints to prevent abuse.
- Updated researcher and publication handling to ensure better validation and error management.

backend/app/services/sync_service.py

@@ -8,12 +8,23 @@ from app.db.repositories.researcher_repository import ResearcherRepository
 from app.db.repositories.publication_repository import PublicationRepository
 from app.db.repositories.syncjob_repository import SyncJobRepository
 
+# ---------------------------------------------------------
+# Clase de servicio de sincronización
+# ---------------------------------------------------------
 
 class SyncService:
 
+    # ---------------------------------------------------------
+    # Función auxiliar: inicializar el servicio de sincronización
+    # ---------------------------------------------------------
+
     def __init__(self):
         self.orcid_client = ORCIDClient()
 
+    # ---------------------------------------------------------
+    # Función auxiliar: sincronizar las publicaciones de un investigador
+    # ---------------------------------------------------------
+
     def sync_researcher(self, db: Session, orcid_id: str):
         """
         Sincroniza las publicaciones de un investigador con manejo robusto de errores.
@@ -109,6 +120,10 @@ class SyncService:
             "total": new_records + updated_records
         }
 
+    # ---------------------------------------------------------
+    # Función auxiliar: sincronizar y obtener investigador + publicaciones
+    # ---------------------------------------------------------
+
     def sync_and_get_full(self, db: Session, orcid_id: str):
         """
         Sincroniza (si es necesario) y devuelve investigador + publicaciones.