Backfill the 161 legacy rows, then VALIDATE the CSV constraint

[niel-cody]

Migration 001 is applied. docs_document_approved_needs_csv_fields was added NOT VALID — without that the migration aborted, because all 161 legacy rows land at status='published' with no slug, hubspot_category, hubspot_subcategory or summary (verified: 161 rows, 0 summaries).

The constraint is enforced on every insert/update from now on; the 161 are grandfathered.

Known friction: NOT VALID still checks on UPDATE, so editing a legacy row (e.g. caching body_html during triage) fails until it carries the four fields. That will bite the reconcile branch.

When backfilled or retired:

alter table public.docs_document validate constraint docs_document_approved_needs_csv_fields;