chore(i18n): drop legacy free-text country/nationality columns

Test-data only — no production migration needed (per earlier decision).
Schema is now ISO-only; readers convert ISO codes to localized names where
human-readable output is required (EOI documents, invoices, portal).

Migration 0016 drops:
  - clients.nationality
  - companies.incorporation_country
  - client_addresses.{state_province, country}
  - company_addresses.{state_province, country}

Code paths that previously read free-text values now read the ISO column
and pass through `getCountryName()` / `getSubdivisionName()` for rendering.
Document templates ({{client.nationality}}), portal client view, EOI/
reservation-agreement contexts, and invoice billing addresses all updated.

Public yacht-interest endpoint (/api/public/interests) drops the legacy
fields from its insert path and writes ISO codes only. The Zod validators
no longer accept the legacy fields — older website builds posting raw
'incorporationCountry' / 'country' / 'stateProvince' will get 400s.
Server-side phone normalization is unchanged.

Seed data updated to use ISO codes (GB/FR/ES/GR/SE/IT/GH/MC/PA), spread
across continents to keep test fixtures realistic.

Test assertions updated to match the new render shape (e.g.
'United States' not 'US', 'California' not 'CA').

Vitest: 741 -> 741 (unchanged count; assertions updated, no new tests).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/lib/services/reservation-agreement-context.ts

@@ -6,6 +6,7 @@ import { berthReservations } from '@/lib/db/schema/reservations';
 import { clients } from '@/lib/db/schema/clients';
 import { ports } from '@/lib/db/schema/ports';
 import { yachts } from '@/lib/db/schema/yachts';
+import { getCountryName } from '@/lib/i18n/countries';
 import { NotFoundError } from '@/lib/errors';
 
 export type ReservationAgreementContext = {
@@ -100,7 +101,7 @@ export async function buildReservationAgreementContext(
     client: {
       id: client.id,
       fullName: client.fullName,
-      nationality: client.nationality,
+      nationality: client.nationalityIso ? getCountryName(client.nationalityIso, 'en') : null,
     },
     yacht: {
       id: yacht.id,