The responsive change had moved `.pageIntro` off flex, which put the information
icon 1.06px off the subtitle's vertical centre and failed the existing geometry
assertion in `plugin-manager.e2e.ts`. Restore the flex row and the button's
`flex: none`, which keeps the 4px gap and the centring. The header still wraps
its action group onto another line, which is what this change is for.
Pin the wrap threshold in both header scenarios. Each records whether the action
group sits beside or below the heading, the plugin scenario asserts the wide and
narrow sides explicitly, and the plugin scenario launches its own scaffold so an
install task left by an earlier test cannot move the threshold between runs.
Yif
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