Add db & pydantic models + set up alembic

backend/app/db.py

@@ -0,0 +1,9 @@
+from sqlmodel import Session, create_engine, select
+from app.config import settings
+from app.models import Client, Supplier
+
+engine = create_engine(str(settings.SQLALCHEMY_DATABASE_URI))
+
+
+def init_db(session: Session) -> None:
+    """"""