The activity heatmap's weekday rows started on the day after the newest day,
so every row changed weekday as days passed. Rows now start on the locale's
first day of the week, and empty cells after the newest day close its week.
Chart axis, readout, and heatmap dates used the CLI's YYYY-MM-DD keys; they
now use the locale's short date, built from the calendar parts so zones west
of UTC keep the same day. Cost lines separate amount and tokens with a middle
dot, matching the Sessions tab.

Provider rows keep the user's configured provider order rather than sorting
by cost, so the order stays consistent across the popup.

Documentation impact: CHANGELOG Unreleased, usage guide Usage & Spend entry,
cost-history heatmap note, regenerated README Usage & Spend capture and the
tour GIF's Usage & Spend frame. Catalog references only; no strings changed.
TODO.md is unaffected.

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