The `| 0` truncation in colorForUserId/colorFor existed to coerce an
undefined user_id to 0, but the settlement API always returns user_id —
only the two BudgetPanel test fixtures omitted it. Add user_id to the
fixtures, switch both helpers to Math.trunc (with a Number.isFinite
guard in colorForUserId preserving the old undefined->0 behaviour), and
drop nothing else: TravelerPicker only ever receives required numbers.
jubnl
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