Third Codex finding on #59, and the same class of bug as the previous
two: the seven-day rows scaled and bolded by tokens while `costPeakLine`
and `costAverageDailyLine` still scanned `point.cost`. A provider tab
could bold 2026-08-14 as the token peak while the label above read
"Peak: 2026-07-18 - $471,76" next to a currency average.

Both helpers now read the selected metric and format with
`tokenCountString` in token mode. The chart's own summary line already
follows it through `displayValue`.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>