feat(channels): add cash channels for Eastern Caribbean and Eurozone Caribbean markets

[altradits]

Summary

Toward #29.

Adds built-in cash channels for Part 1 of the Caribbean (UN M49: 029) regional batch, covering all 8 Eastern Caribbean Currency Union (ECCU) markets using the Eastern Caribbean Dollar (XCD) and 4 French Caribbean collectivities/departments using the Euro (EUR):

Eastern Caribbean Currency Union (XCD)

Authority: Eastern Caribbean Central Bank (ECCB) (Eastern Caribbean Central Bank Agreement Act 1983).

1. Anguilla (AI / XCD): cash_ai_xcd
2. Antigua and Barbuda (AG / XCD): cash_ag_xcd
3. Dominica (DM / XCD): cash_dm_xcd
4. Grenada (GD / XCD): cash_gd_xcd
5. Montserrat (MS / XCD): cash_ms_xcd
6. Saint Kitts and Nevis (KN / XCD): cash_kn_xcd
7. Saint Lucia (LC / XCD): cash_lc_xcd
8. Saint Vincent and the Grenadines (VC / XCD): cash_vc_xcd

French Caribbean (EUR)

Authority: Institut d'Émission des Départements d'Outre-Mer (IEDOM) / European Central Bank (Code monétaire et financier, Art. L711-2; Treaty on the Functioning of the European Union, Art. 349).

9. Guadeloupe (GP / EUR): cash_gp_eur
10. Martinique (MQ / EUR): cash_mq_eur
11. Saint Barthélemy (BL / EUR): cash_bl_eur
12. Saint Martin (French part) (MF / EUR): cash_mf_eur

Implementation Details

• Uses canonical createCashPaymentChannel helper (schema version 2, automation: PaymentChannelAutomation.None, no collection fields).
• Grouped by country in src/channels/<country>/cash.ts.
• Re-exports all schemas from src/index.ts and registers them in builtinPaymentChannels.
• Adds discovery contract tests in test/payment-channels.test.mjs verifying Eastern Caribbean and Eurozone Caribbean markets resolution.
• Refreshes generated registry documentation via npm run docs:generate.

Verification

• npm run check (formatter, TypeScript typecheck, docs check, examples check, and 43/43 tests pass)
• npm pack --dry-run (clean tarball with runtime artifacts only)
• npm run verify:pack (verified on isolated ESM and CommonJS consumers)

[okjodom]

Reviewed: changes follow the declarative cash-channel schema and registry conventions. CI check passes.