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>

tests/integration/invoices-billing-entity.test.ts

@@ -161,9 +161,9 @@ describe('invoices.service — billing entity', () => {
       label: 'Primary',
       streetAddress: '1 Pier Road',
       city: 'Harbor City',
-      stateProvince: 'CA',
+      subdivisionIso: 'US-CA',
       postalCode: '90000',
-      country: 'USA',
+      countryIso: 'US',
       isPrimary: true,
     });
 
@@ -180,7 +180,10 @@ describe('invoices.service — billing entity', () => {
     );
 
     expect(invoice.billingEmail).toBe('bob@example.com');
-    expect(invoice.billingAddress).toBe('1 Pier Road, Harbor City, CA, 90000, USA');
+    // Address is rendered using ISO->name lookup (US-CA -> California, US -> United States).
+    expect(invoice.billingAddress).toBe(
+      '1 Pier Road, Harbor City, California, 90000, United States',
+    );
   });
 
   it('allows caller to override billingEmail and billingAddress', async () => {
@@ -196,9 +199,9 @@ describe('invoices.service — billing entity', () => {
       label: 'Primary',
       streetAddress: '2 Ocean Blvd',
       city: 'Portville',
-      stateProvince: 'FL',
+      subdivisionIso: 'US-FL',
       postalCode: '33101',
-      country: 'USA',
+      countryIso: 'US',
       isPrimary: true,
     });