Add initial work from Codex

backend/app/db/postgres.py

@@ -0,0 +1,27 @@
+from __future__ import annotations
+
+from sqlalchemy import create_engine
+from sqlalchemy.engine import Engine
+from sqlalchemy.orm import Session, sessionmaker
+
+from app.core.config import settings
+from app.db.postgres_models import Base
+
+
+def create_postgres_engine() -> Engine:
+    return create_engine(
+        settings.postgres_connection_url,
+        pool_pre_ping=True,
+        pool_recycle=3600,
+        future=True,
+    )
+
+
+def initialize_postgres_schema(engine: Engine) -> None:
+    Base.metadata.create_all(bind=engine)
+
+
+def create_postgres_session_factory(engine: Engine) -> sessionmaker[Session]:
+    return sessionmaker(
+        bind=engine, autoflush=False, autocommit=False, expire_on_commit=False
+    )