* style(ui): refine popup visual hierarchy

Remove framing the Plasma dialog already provides: the popup's nested inner
outline and the separator under the tab strip. Mark tab selection with a
clearly visible surface alone, so a provider tab's underline is only its
quota meter and a partly filled bar no longer reads as a selected tab.
Overview, session, and spend rows share borderless surfaces and tiles.

Keep quotas ahead of cost in the provider detail view: the cost section
drops the day count the axis and summary already state, uses a flat metric
selector and details toggle, and sets its estimate note in small type. A
described incident shows only its banner; the header badge remains for an
incident without a description. The header separates account and plan.

The activity heatmap names each weekday row in the system locale through a
new pure CostPresentation.spendHeatmapRowWeekdays helper, and widens cells
up to a 2:1 tile. Rows stay unlabelled when days are not calendar aligned.

Documentation impact: CHANGELOG Unreleased, usage guide (tabs, heatmap,
incident badge), cost-history heatmap note, README capture notes, and the
regenerated README popup captures and tour GIF. The translation template
loses one source reference; no strings changed. TODO.md is unaffected.

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

* docs(ui): describe the incident banner as the single carrier

Status text always names the incident severity, even when the CLI omits a
description, so the detail banner carries every current incident and the
header badge is only a fallback for an incident without banner text. Correct
the comment, test, usage guide, and changelog that promised the badge for
undescribed incidents.

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

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