Add Ladybug graph demo

[adsharma]

Summary

• add a Ladybug decorator for fquery nodes and graph-level schema registration
• add a runnable ReviewGraph demo covering save/write, Cypher generation, Arrow table registration, and query_as_arrow
• preserve Cypher label casing for Ladybug table labels

Validation

• .venv/bin/python -m pytest -q
• .venv/bin/python examples/ladybug_demo.py

Needs ladybug >= 0.17.0