feat: enhance authentication and publication download tracking

- Added JWT authentication support with configurable secret and expiration.
- Introduced optional API key validation for endpoints.
- Implemented tracking of publication downloads by researchers, storing records in a new PublicationDownload model.
- Updated export endpoints to conditionally register downloads based on user authentication.
- Enhanced researcher search response to indicate if publications were downloaded by the current user.
- Updated environment configuration to include new JWT settings.

backend/app/main.py

@@ -4,6 +4,7 @@ from fastapi.middleware.cors import CORSMiddleware
 from app.db.session import init_db
 from app.api.researchers import router as researchers_router
 from app.api.export import router as export_router
+from app.api.auth import router as auth_router
 from app.scheduler.sync_scheduler import start_scheduler
 
 
@@ -39,6 +40,7 @@ def health():
 # ---------------------------------------------------------
 app.include_router(researchers_router, prefix="/api")
 app.include_router(export_router, prefix="/api")
+app.include_router(auth_router, prefix="/api")
 
 
 # ---------------------------------------------------------