WOOA7S-1497: add Videos widget backed by Jetpack Stats

[Nikschavan]

Proposed changes

Ports the Videos widget from the Jetpack Stats module into the Premium Analytics dashboard, backed by the Jetpack Stats API.

• data package: adds a stats-fetch API client that goes through the stats-admin proxy (/jetpack/v4/stats-app/sites/{blog_id}/stats/{resource}), plus statsQuery/statsVideoPlaysQuery query builders and useStatsVideoPlays/useStatsBlogId hooks. The blog ID is resolved once from /jetpack/v4/connection/data and cached for the page lifetime; queries use skipToken while the blog ID or report date is unresolved.
• widgets-toolkit: adds VideosWidget (leaderboard chart of most played videos with comparison support) and a buildVideoPlaysData helper, with loading/refetching overlays and empty/error states.
• premium-analytics plugin: registers the jpa/videos dashboard widget (render entry, widget.json, widget.ts with a configurable max attribute). The render entry defaults to an all-time report range until the host can pass the site launch date.
• chart empty state: centers the empty state across the full widget width instead of the chart column.
• query client provider: adds a withDevtools prop so React Query devtools render once at the page level instead of per widget.
• icons: adds a video icon used for the chart empty state.

Note: the diff also carries the "add dynamic widget registry and REST endpoint" commit until the base branch catches up with it.

Related product discussion/links

• WOOA7S-1497

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

No.

Testing instructions

• Set up a Jetpack-connected site with the Premium Analytics plugin active, ideally one with VideoPress/video traffic.
• Go to the Premium Analytics dashboard and open the widget picker.
• Add the Videos widget.
• Verify it renders a leaderboard of the most played videos, sourced from Jetpack Stats (check the network tab for requests to /jetpack/v4/stats-app/sites/{blog_id}/stats/video-plays).
• Change the Maximum videos attribute and verify the list respects the limit.
• On a site with no video plays, verify the empty state copy renders centered across the widget instead of the chart.

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