feat: scaffold FastAPI app, config, and SQLite models

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/app/db.py

@@ -0,0 +1,24 @@
+from collections.abc import Generator
+
+from sqlalchemy import create_engine
+from sqlalchemy.orm import DeclarativeBase, Session, sessionmaker
+
+from app.config import settings
+
+engine = create_engine(
+    settings.db_url,
+    connect_args={"check_same_thread": False},
+)
+SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
+
+
+class Base(DeclarativeBase):
+    pass
+
+
+def get_db() -> Generator[Session, None, None]:
+    db = SessionLocal()
+    try:
+        yield db
+    finally:
+        db.close()