Credit balances that round up to a whole number at one fractional digit
kept the digit (99.95 printed as 100.0). The count formatter now drops
the fractional digit when the rounded figure is whole, using the
locale decimal mark, and magnitudes past 1e21 skip digit grouping
since Number.toFixed returns exponential notation there.

The main.qml helper delegates to the pure CostPresentation.formatCount
so the rounding stays covered by direct QtTests; the UI regression
check pins the delegation like the Guards.js precedent.