b5495be1 - Collapse the two IBAN switch buttons into one cycle

[TaprootFreak]

Summary

The buy payment-details IBAN row rendered two adjacent switch controls whenever a verified Bank Frick personal IBAN also had a Yapeal alternative: the collection-account SWAP toggle and the provider BANK toggle. That is one job. This change keeps a single SWAP button that cycles through every IBAN actually available on the current quote:

1. the personal IBAN of the current quote
2. the Bank Frick collection IBAN, when getOfferableCollectionIban offers one
3. the other personal-IBAN provider, when personalIbanProviderSwitch is passed

Collection remains a local display change (QR and invoice rewrite unchanged). A provider step still calls onSwitch so the screens request a fresh quote pinned to that provider. Collection-only and provider-only rows keep their previous behaviour, except the provider-only control now uses the same SWAP icon.

Public PaymentInformationContent props are unchanged. Existing translation keys are reused. The provider callback lives on the discriminated switch target; the cycle helper stays file-private.

Tests

Per-file coverage for every instrumented file this pull request touches, measured with:

CI=true npm test -- --watchAll=false --coverage --collectCoverageFrom='src/components/payment/payment-info-buy.tsx' --testPathPattern='payment-info-buy'

File	Stmts	Branch	Funcs	Lines
src/components/payment/payment-info-buy.tsx	100	100	100	100

33 unit tests in the payment-info-buy suites passed. Combined-cycle cases pin exactly one switch button, a local first click, and a provider onSwitch on the second click.

The /buy and /buy/info Playwright scenarios step through collection first on a verified Frick CHF quote, then switch to Yapeal. Their four provider-toggle baselines (buy-chf-provider-toggle-*, buy-info-provider-toggle-*) are regenerated and show one SWAP control. The matching full-stack tests in e2e-stack/specs/buy.spec.ts assert that Payment Information never renders more than one IBAN switch button.

[TaprootFreak]

EN: Ready after 4 review passes.
DE: Bereit nach 4 Review-Durchläufen.

Details

Review passes:

1. Exported cycle helper existed only so a test could hit an unreachable throw. The provider callback now lives on the discriminated switch target; the helper is file-private.
2. The matching full-stack /buy and /buy/info tests assert that Payment Information never renders more than one IBAN switch button.
3. No remaining code findings.
4. Provider-toggle Playwright baselines were regenerated and show one SWAP control instead of SWAP plus bank icons. Collection-only baselines are unchanged.

Comments: none open besides this note (no review threads).
Mergeability: mergeable: MERGEABLE at head 32d55263.
CI at that head: Build and test, Full-stack E2E, review, CodeQL, and CodeQL Analyze jobs all SUCCESS. Handbook image check is draft-skipped by design and runs on ready.