Run the MVP acceptance checklist against 1.2.0

[ihistand]

Run the by-hand real-user acceptance checklist (SQLAnvil/docs mvp_user_test_checklist.md) against 1.1.2 on real Postgres + Supabase. A 1.0.1 + Windows pass is on record; this pass should cover the newer surface — named connections (BigQuery source) and the introspect credentials format (the connections map in .df-credentials.json).