fix(backend): rename retriver directory to retriever

Fixes typo in directory name and updates all import paths:
- Renamed surfsense_backend/app/retriver/ to surfsense_backend/app/retriever/
- Updated imports in db.py
- Updated imports in connector_service.py

surfsense_backend/app/db.py

@@ -25,8 +25,8 @@ from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker, create_asyn
 from sqlalchemy.orm import DeclarativeBase, Mapped, declared_attr, relationship
 
 from app.config import config
-from app.retriver.chunks_hybrid_search import ChucksHybridSearchRetriever
-from app.retriver.documents_hybrid_search import DocumentHybridSearchRetriever
+from app.retriever.chunks_hybrid_search import ChucksHybridSearchRetriever
+from app.retriever.documents_hybrid_search import DocumentHybridSearchRetriever
 
 if config.AUTH_TYPE == "GOOGLE":
     from fastapi_users.db import SQLAlchemyBaseOAuthAccountTableUUID