TicketBAI: enable exempt reasons & not-subject transactions

[StefanKert]

Summary

Implements market-es#97 — replaces the hard-coded subject / not exempt / S1 TicketBAI branch with a mapper-driven build of all <Sujeta>/<Exenta>, <Sujeta>/<NoExenta> and <NoSujeta> sub-branches based on the charge item's NatureOfVat.

• New TicketBaiNatureOfVatMapping centralises the NatureOfVatES → (ClaveRegimen, Branch, CausaExencion?, TipoNoExenta?, CausaNoSujeta?) table from the issue.
• TicketBaiFactory.GetFacturaDetails now groups items by NatureOfVat, builds the correct branch combination, and applies the same logic inside the foreign-recipient <Entrega> / <PrestacionServicios> split.
• Claves is derived from the items (exports → 02, mixed → both 01 and 02) instead of being pinned to Item01.

Coverage of the spec table

NN	NatureOfVatES	Result
[10] Exports	ExteptArticle21	<Exenta CausaExencion=E2>, Claves 02
[11] Intra-community delivery	ExteptArticle25	<Exenta CausaExencion=E5>, Claves 01
[13] Treated as exports	ExteptArticle22	<Exenta CausaExencion=E3>, Claves 02
[14] Customs / tax-regulation	ExteptArticle23And24	<Exenta CausaExencion=E4>, Claves 02
[20] Not subject — location	NotSubjectLocationRules	<NoSujeta Causa=RL>
[21] Not subject — Art. 7/14	NotSubjectArticle7and14	<NoSujeta Causa=OT>
[30] Exempted domestic	ExteptArticle20	<Exenta CausaExencion=E1>
[31] Other exemptions	ExteptOthers	<Exenta CausaExencion=E6>
[50] Reverse charge	ReverseCharge	<NoExenta TipoNoExenta=S2>

Out of scope (matches the issue's open questions)

• NN [60] (IE — foreign tax IPSI/IGIC) and NN [80] (VT — third-party transactions) have no ChargeItemCaseNatureOfVatES value yet; the mapper throws NotSupportedException if those ever show up.
• The Entrega vs. PrestacionServicios split still uses the existing TypeOfService-based filter — the open question about queue-es carrying explicit goods-vs-services is unresolved upstream.
• No additional spec validation beyond what the mapper enforces by construction.

Test plan

• dotnet test scu-es/test/fiskaltrust.Middleware.SCU.ES.UnitTest — 17 new tests pass (11 mapping + 7 factory). Pre-existing VeriFactuTest certificate-dependent cases unchanged.
• Smoke-check against the Araba / Bizkaia / Gipuzkoa sandbox endpoints with a domestic exempt + not-subject + reverse-charge invoice (requires local certificates, out of CI scope).

🤖 Generated with Claude Code

[github-actions]

SCU.ES Test Results

  2 files    2 suites   0s ⏱️
 81 tests  78 ✅ 3 💤 0 ❌
162 runs  156 ✅ 6 💤 0 ❌

Results for commit a843759.

♻️ This comment has been updated with latest results.