First BillModal decompose step: the collapsible Debt/Snowball fields (interest
rate, current balance, minimum payment, snowball visibility) move to
client/components/bill-modal/DebtDetailsSection.jsx as a presentational
component; state stays in the parent (the save action reads it). Behavior-
preserving — BillModal 1723 -> 1637 lines; build + client tests green.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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