The provider cost chart dates its days in the locale's short format, but
the history rows, the peak line, the latest-day summary, and the
selected-day details title showed the CLI's YYYY-MM-DD keys. All of them
now use the chart's format; other labels stay as the CLI sent them.

The calendar key to local date conversion moves into ProviderNormalizer,
so the chart and the cost text share it. The static check for the details
title only ever matched its second fragment; it now checks both titles.

Documentation impact: CHANGELOG Unreleased and the usage guide's cost
entry. TODO.md is unaffected.

Co-authored-by: Claude Opus 5.5 (1M context) <noreply@anthropic.com>