feat: add database setup module

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

db.py

@@ -0,0 +1,18 @@
+from sqlalchemy import create_engine
+from sqlalchemy.orm import sessionmaker
+
+from models import Base
+
+DB_PATH = "sqlite:///wordsearch.db"
+
+
+def get_engine(db_url=None):
+    return create_engine(db_url or DB_PATH)
+
+
+def get_session_factory(engine):
+    return sessionmaker(bind=engine)
+
+
+def init_db(engine):
+    Base.metadata.create_all(engine)