Extends public.language_code with the Euskera (Basque, ISO 639-1) label.
Plan §20.1 was written against a CHECK-constraint mental model; the
actual gate is the ENUM from migration 001, so the right primitive is
ALTER TYPE … ADD VALUE. End-user contract is identical — 'eu' accepted,
'fr' rejected — and rejection surfaces as the canonical 22P02
invalid_text_representation error.
pgTAP `supabase/tests/020_users_language_eu.sql` (5 assertions, LANG-EU-
T01..T05) pins both ends: ENUM membership and UPDATE round-trip on Ana.
Hand-curated database.ts widened to `'en' | 'es' | 'eu'`. The supabase
CLI isn't on this host, so db-types regen is the manual edit per the
recipe's fallback path.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>