docs: add Washington DC stock analysis notebook

[nllong]

Summary

• Add an executed notebook for Washington, DC office and multifamily stock analysis.
• Search ComStock office and ResStock multifamily records, plot stock characteristics, download high-site-EUI examples, and plot demand/monthly end-use profiles.
• Generate transparent measure recommendations from dominant time-series end uses and matching available upgrade packages.

Validation

• uv run jupyter nbconvert --to notebook --execute --inplace 02_washington_dc_stock_analysis.ipynb
• uv run ruff check .
• uv run pytest tests/ -m "unit" -v
• uv run mypy