Add app scaffold and workflows

app/backend/core/database.py

@@ -0,0 +1,14 @@
+"""Database connection placeholders."""
+
+from contextlib import contextmanager
+from typing import Iterator
+
+
+@contextmanager
+def get_db() -> Iterator[None]:
+    """
+    Yield a database session placeholder.
+
+    Replace with a real session (e.g., SQLAlchemy) when persistence is added.
+    """
+    yield None