HDPI-4195: Instalment payment screen

[andrewdami11]

Jira link

See HDPI-4195

BACKEND PR

Screenshots

Change description

This branch implements the instalment-payment flow for respond-to-claim rent arrears journeys and
aligns draft-save, restoration, and navigation with CCD-backed data patterns.

• Added the instalment flow steps and route wiring in respond-to-claim:

  • installment-payments
  • how-much-afford-to-pay
  • updated your-household-and-circumstances interstitial content and registration

• Updated route transitions in flow.config.ts so rent-arrears users selecting no on
  repayments-agreed are routed into instalment questions, with progression to
  your-household-and-circumstances after the branch.

• Implemented and refined CCD mapping/persistence for payment agreement data:

  • submit and draft-save handling in how-much-afford-to-pay/index.ts and
    autoSaveDraftToCCD.ts
  • mapping and typing updates in ccdCase.interface.ts

• Added/updated previous-step logic for household-and-circumstances in
  yourHouseholdCircumstancesPreviousStep.ts, then wired it in flow.config.ts.

• Added/updated EN/CY translations for:

  • installmentPayments
  • howMuchAffordToPay
  • yourHouseholdAndCircumstances

• Updated tests and UI page-data fixtures for the changed flow, draft-save mapping, and
  step restoration/navigation.

Testing done

Evidence from this branch diff includes updated/added automated tests:

• src/test/unit/middleware/autoSaveDraftToCCD.test.ts
• src/test/unit/steps/respond-to-claim/installment-payments.test.ts
• src/test/unit/steps/respond-to-claim/installments.test.ts
• src/test/unit/steps/respond-to-claim/yourHouseholdCircumstancesPreviousStep.test.ts

Security Vulnerability Assessment

CVE Suppression: Are there any CVEs present in the codebase (either newly introduced or pre-existing) that are being intentionally suppressed or ignored by this commit?

• Yes
• No

Checklist

• commit messages are meaningful and follow good commit message guidelines
• README and other documentation has been updated / added (if needed)
• tests have been updated / new tests has been added (if needed)
• Does this PR introduce a breaking change