feat(fase-20): migration 028 — language_code ENUM gains 'eu'

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>

packages/types/src/database.ts

@@ -4,7 +4,7 @@
 
 export type Json = string | number | boolean | null | { [key: string]: Json | undefined } | Json[];
 
-export type LanguageCode = 'en' | 'es';
+export type LanguageCode = 'en' | 'es' | 'eu';
 export type AvatarTypeEnum = 'initials' | 'emoji' | 'upload';
 export type MemberRoleEnum = 'admin' | 'member' | 'guest';
 export type ListStatusEnum = 'active' | 'completed' | 'archived';