Supersedes #275986 and fixes its approach: that PR updates the withholding rates **in place** on the existing tax records (`ret_10_income_person`, `ret_10_income_rent`, `ret_2_income_person`, and repurposes `ret_2_income_transfer` into a different concept). Those records exist in production databases with posted history behind them, and the pre-law rates remain legally applicable to operations dated before the law's entry into force, so rewriting them breaks prior-period postings, corrections and reports. Following the approach used for equivalent legal rate changes in other localizations on stable branches (`l10n_ee`, `l10n_sk`, `l10n_fi`), this PR adds **new taxes** for the new rates, keeps the pre-law taxes active, archives the superseded 27% remittance withholding, gives the new 15% withholding its own payable account instead of reusing the one tied to L253-12, and leaves the module authorship untouched.

## Description

Dominican Republic Law 30-26 ("medidas pro-crecimiento económico, simplificación fiscal y mitigación de la crisis internacional"), enacted on June 18, 2026, amends several provisions of the Tax Code that affect taxes shipped with the `l10n_do` chart template:

| Concept | Before | After | Effective |
|---|---|---|---|
| ISR withholding on fees/services provided by individuals (art. 309 b) | 10% | 15% (payment on account) | July 2026 |
| ISR withholding on rents paid to individuals (art. 309 a) | 10% | 15% (single and final) | July 2026 |
| ISR withholding on payments abroad for software licenses/subscriptions, royalties, online advertising and cloud data storage (arts. 305-1 / 305-2) | 27% (general remittance rate) | 15% (single and final) | June 18, 2026 |
| ISR withholding on technical services provided by individuals (art. 309 rate over the 20% presumed base of art. 70, Regulation 139-98) | 2% effective | 3% effective | July 1, 2026 (DGII notice 10-26) |

Changes:

- New taxes `ret_15_income_person` and `ret_15_income_rent`. The pre-law 10% taxes are kept active since their rates remain applicable to operations dated before the law.
- New taxes `ret_3_income_person` and `ret_3_income_transfer` for the effective 3% withholding on technical services, posting to a new payable account `l10n_do_21030311` ("Other Withholdings (L30-26)") since their pre-law counterparts' accounts are tied to previous regulations; the pre-law 2% taxes also remain active.
- New tax `ret_15_income_remittance_tech`, posting to a new payable account `l10n_do_21030310` ("ISR Withheld on Remittances Abroad (L30-26)"), since the existing remittance account is tied to L253-12.
- `ret_27_income_remittance` is deactivated in the template, superseded by the new reduced withholding.

The new tax names follow the module's existing convention of tagging the enforcing law (as with "(L253-12)").

No changes are needed in the tax report: the ISR withholding taxes only distribute to payable accounts, without tax grids.

Scope note: Law 30-26 also raises the tax on checks and electronic transfers from 1.5‰ to 2.0‰ (art. 382 of Law 288-04, as amended), deliberately left out here: it is not an invoiceable tax — banks withhold it directly on account debits, so it is handled outside invoice accounting.

References:
- https://presidencia.gob.do/leyes/ley-30-26
- https://www.hacienda.gob.do/ley-30-26-no-dispone-impuestos-por-suscripciones-de-ciudadanos-a-plataformas-digitales-reduce-de-27-a-15-la-retencion-a-empresas-que-contratan-servicios-tecnologicos-en-el-exterior/