feat(channels): add cash channels for Eastern Asian markets

[altradits]

Summary

Toward #29.

Adds built-in cash channels for Eastern Asia (UN M49: 030), covering all 8 sovereign markets and administrative territories across the region:

Eastern Asian Markets

1. China (CN / CNY): cash_cn_cny — Chinese Yuan / Renminbi (People's Bank of China / Law of the People's Republic of China on the People's Bank of China, Order of the President No. 12; Regulations of the PRC on the Administration of Renminbi, State Council Decree No. 280)
2. Hong Kong SAR (HK / HKD): cash_hk_hkd — Hong Kong Dollar (Hong Kong Monetary Authority / Legal Tender Notes Issue Ordinance Cap. 65; Coinage Ordinance Cap. 67; Basic Law of HKSAR Art. 111)
3. Japan (JP / JPY): cash_jp_jpy — Japanese Yen (Bank of Japan / Bank of Japan Act, Act No. 89 of 1997, Art. 46; Currency Units and Issuance Act, Act No. 42 of 1987)
4. Democratic People's Republic of Korea (KP / KPW): cash_kp_kpw — North Korean Won (Central Bank of the DPRK / Law of the DPRK on the Central Bank; Decision of the Standing Committee of the Supreme People's Assembly)
5. Republic of Korea (KR / KRW): cash_kr_krw — South Korean Won (Bank of Korea / Bank of Korea Act, Act No. 13822, Arts. 47, 48)
6. Mongolia (MN / MNT): cash_mn_mnt — Mongolian Tögrög (Bank of Mongolia / Law of Mongolia on the Central Bank, Arts. 7, 8, 9)
7. Macao SAR (MO / MOP): cash_mo_mop — Macanese Pataca (Monetary Authority of Macao / Decree-Law no. 7/95/M; Basic Law of Macao SAR Art. 108)
8. Taiwan (TW / TWD): cash_tw_twd — New Taiwan Dollar (Central Bank of the Republic of China (Taiwan) / Central Bank Act Art. 13; Regulations for the Issuance of the New Taiwan Dollar Notes and Coins)

Implementation Details

• Uses canonical createCashPaymentChannel factory (schemaVersion: 2, automation: PaymentChannelAutomation.None, no collection fields, standard copy/display detail rows).
• Source layout follows src/channels/<country>/cash.ts per channel conventions.
• Registered in src/channels/index.ts and re-exported from src/index.ts.
• Included in builtinPaymentChannels and validated against completeness checks in test/payment-channels.test.mjs.
• Added market discovery and regression test suite registry exposes built-in cash channels for Eastern Asian markets.
• Refreshed generated documentation and JSON registry via npm run docs:generate.

Authoritative Documentation & Primary Sources

• China: People's Bank of China (中国人民银行) http://www.pbc.gov.cn/ (Law of the People's Republic of China on the People's Bank of China; Regulations of the PRC on the Administration of Renminbi).
• Hong Kong SAR: Hong Kong Monetary Authority (香港金融管理局) https://www.hkma.gov.hk/ (Legal Tender Notes Issue Ordinance Cap. 65; Coinage Ordinance Cap. 67; Basic Law of HKSAR Art. 111).
• Japan: Bank of Japan (日本銀行) https://www.boj.or.jp/ (Bank of Japan Act, Act No. 89 of 1997, Art. 46; Currency Units and Issuance Act, Act No. 42 of 1987).
• Democratic People's Republic of Korea: Central Bank of the Democratic People's Republic of Korea (조선민주주의인민공화국 중앙은행) (Law of the DPRK on the Central Bank; Decision of the Standing Committee of the SPA).
• Republic of Korea: Bank of Korea (한국은행) https://www.bok.or.kr/ (Bank of Korea Act, Act No. 13822, Arts. 47, 48).
• Mongolia: Bank of Mongolia (Монголбанк) https://www.mongolbank.mn/ (Law of Mongolia on the Central Bank, Arts. 7, 8, 9).
• Macao SAR: Monetary Authority of Macao (Autoridade Monetária de Macau / 澳門金融管理局) https://www.amcm.gov.mo/ (Decree-Law no. 7/95/M; Basic Law of Macao SAR Art. 108).
• Taiwan: Central Bank of the Republic of China (Taiwan) (中央銀行) https://www.cbc.gov.tw/ (Central Bank of the Republic of China (Taiwan) Act Art. 13; Regulations for the Issuance of the New Taiwan Dollar Notes and Coins).

Verification

• npm run check (formatter, TypeScript typecheck, docs check, examples check, and 57/57 tests pass)
• npm pack --dry-run (clean tarball with runtime artifacts only)
• npm run verify:pack (verified on isolated ESM and CommonJS consumers)