Two readability defects in the cost surfaces.

- Money rendered as a bare digit run, so four- and five-figure totals read as
  "$3833.55". Number.toLocaleString with 'f' localizes the decimal mark but
  adds no group separators, so groupedDecimalString applies the grouping using
  the active locale's separators. Amounts now render "$3.833,55" under an
  Italian locale and "$3,833.55" under en_US. This reaches every amountString
  caller, including the provider detail cost sections.

- Every Usage & Spend provider row repeated "Last 90 days:", which the range
  selector directly above already states, and which is guaranteed consistent
  because costSnapshotMatchesSelectedRange filters the rows to the selected
  range. Normalized token costs now also expose windowValueLine, the same
  figures without the window label; costLine keeps the label for the provider
  detail view, which has no range selector of its own.

Static assertions cover both. Translation template regenerated.