Admin pages content appears squashed / incorrectly sized

[JohnMcLear]

Content inside the admin pages (plugin manager, settings editor, etc.) renders in a visibly squashed layout — probably an inner container that has been resized or had its dimensions constrained unintentionally.

Reproduction

1. Log in to the admin interface (`/admin`).
2. Navigate to any admin page (Plugin manager, Settings, etc.).
3. Observe the content area.

Expected

Content fills the admin viewport with proper breathing room; panels and tables sized for readable use.

Notes

• Appears to be pre-existing; not caused by the open fix(a11y): dialog semantics, focus management, icon labels, html lang #7584 a11y PR, which only touched pad/index/timeslider templates.
• Discovered while auditing aria coverage across pages for fix(a11y): dialog semantics, focus management, icon labels, html lang #7584.