test: cover SettlementModal reason mapping

[singhvishalkr]

Summary

• add table-driven coverage for every SettlementModal ineligible-reason category
• cover mixed-case and whitespace normalization for not-matured responses
• keep the change scoped to the existing production modal test file

Closes #589

Verification

• npm.cmd ci
• npm.cmd test -- tests/SettlementModal.test.tsx
• npx.cmd eslint tests/SettlementModal.test.tsx
• git diff --check

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