WOOA7S-1508: Port Stats Most popular time widget

[kangzj]

Fixes WOOA7S-1508

Proposed changes

• Ports the Jetpack Stats "Most popular time" highlight into a registered Premium Analytics widget (jpa/most-popular-time, category stats, framed presentation).
• Shows the peak hour for views and its share of the total (hour rendered via <Text>, share via MetricWithComparison value-only), above a bar chart of views across the day rendered with the toolkit BarChart.
• Data comes from the existing useStatsInsights hook (stats/insights proxy). The insights endpoint reports across the whole lifetime of the site, so there is no date range and no comparison period — WithComparison renders identically to Default, which the story documents.
• Follows the Stats-widget contract: two-component split with WidgetRoot, WidgetLoadingOverlay only when loading with no data, host-owned chrome (no body heading), all strings through __( …, 'jetpack-premium-analytics' ), CSS Modules with --wpds-* tokens only, and the picker-preview aspect-ratio block.
• Adds three Storybook stories (Default, WithComparison, WidgetDashboardWithWidget) per the AGENTS.md template. Central mocks don't cover stats/insights, so a story-scoped apiFetch middleware mocks it inside the story file (the shared register-report-mocks is untouched).

Scope is additive only: the new widgets/most-popular-time/** folder plus a changelog entry. The Storybook widgets root is already registered in projects.js.

Related product discussion/links

• WOOA7S-1508

Does this pull request change what data or activity we track or use?

No. It reuses the existing stats/insights proxy endpoint via the existing useStatsInsights data hook; no new tracking.

Testing instructions

• Live-dashboard verification pending — handled centrally; Storybook + audit + eslint + build pass locally.
• In Storybook, open Packages / Premium Analytics / Widgets / MostPopularTime and confirm:
  • Default shows the peak-hour highlight, its share of views, and the hourly bar chart.
  • WithComparison renders identically (insights has no comparison period).
  • WidgetDashboardWithWidget renders the widget in the real dashboard chrome (framed card).
• Local checks that pass: pnpm exec eslint (clean), stylelint (clean), tsc --noEmit (clean), jetpack build packages/premium-analytics --deps (succeeds), and /widget-audit most-popular-time (no violations).

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Code Coverage Summary

This PR did not change code coverage!

That could be good or bad, depending on the situation. Everything covered before, and still is? Great! Nothing was covered before? Not so great. 🤷

Full summary · PHP report

[kangzj]

Live dashboard verification — Most popular time

Rendered on the connected Premium Analytics dashboard (Insights tab, raven env, blog 254382195) with real data and zero console errors.