feat: add SQLAlchemy database layer with get_db dependency

app/core/database.py

@@ -0,0 +1,22 @@
+from sqlalchemy import create_engine
+from sqlalchemy.orm import DeclarativeBase, Session, sessionmaker
+
+from app.core.config import get_settings
+
+settings = get_settings()
+
+_connect_args = {"check_same_thread": False} if settings.DATABASE_URL.startswith("sqlite") else {}
+engine = create_engine(settings.DATABASE_URL, connect_args=_connect_args)
+SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
+
+
+class Base(DeclarativeBase):
+    pass
+
+
+def get_db() -> Session:
+    db = SessionLocal()
+    try:
+        yield db
+    finally:
+        db.close()