fix(newsletters): upgrade DataViews to 16 and fix list styling

[thomasguillot]

Summary

Upgrades the Newsletters admin-shell DataViews lists to @wordpress/dataviews@16.0.0 and fixes the resulting list styling.

The admin-shell bundle was compiling @wordpress/dataviews@10.3.0 (DEWP bundles dataviews rather than externalizing it). That older version drew a stray <hr> separator in the row Actions kebab and used an older table column-sizing model. Bumping to 16.0.0 removes the separator and matches core's current DataViews behavior. The bump is scoped to this plugin — the workspace root stays on 10.x, and webpack resolves the plugin's own 16.0.0 copy.

Changes

• package.json — add @wordpress/dataviews: ^16.0.0 devDependency (plus the matching pnpm-lock.yaml entry). Removes the stray Actions-menu separator.
• style.scss
  • Add .dataviews-view-table col.dataviews-view-table__col-first-data { width: auto !important; } to re-assert the primary column as flexible. newspack-plugin's global commons.css still ships dataviews 10.x CSS whose col:not(.dataviews-view-table__col-primary){width:1%} rule wrongly matches 16.x's renamed __col-first-data column, which otherwise left no column to absorb table slack.
  • Remove two overrides now redundant on 16.x (a .components-base-control margin reset and a pagination select line-height), each verified dead by toggling live in the browser.
  • Reorganize the file into logical sections, add two SASS mixins (inline-icon, flex-column-fill), and nest the previously-flat .newspack-newsletters-quick-edit-modal__* selectors under one block.

Testing

• Verified the SCSS refactor compiles to equivalent CSS — identical declaration count (2914) and rule count (1707) before/after.
• lint:scss passes.
• Browser-checked all five DataViews screens (Newsletters, Ads, Advertisers, Layouts lists + the Layout picker modal): separator gone, column widths correct, Quick Edit slide-in panel and reduced-motion behavior intact.
• Reviewed by Codex and Claude — 0 findings.