Align callout blocks with article content width

[aaronpowell]

Callout blocks, such as Caution, use excessive horizontal margins on smaller screens. Make them match the article text width and alignment while preserving appropriate internal padding and responsive gutters.

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[aaronpowell]

Fixed in 4ecde56.

Root cause: the callout (.proTip, used for Note/Tip/Caution admonitions in Learning Hub articles and the "Maintained outside this repository" notice on external Plugin Detail pages) had its own 32px horizontal margin. In the design prototype this callout sits as a sibling of .articleSection (which has no horizontal padding of its own), so the margin exists specifically to align it with the section's own 32px padding. Our port always renders the callout nested inside an already-padded .articleSection, so the margin doubled up with that padding and made the callout narrower than the surrounding text -- worst on narrow/mobile viewports.

Removed the horizontal margin (kept only the bottom spacing) in both dotnet-upgrade.module.css and github-copilot-app.module.css. Verified on a Learning Hub workshop article (desktop + 390px mobile) and an external Plugin Detail page -- the callout now lines up edge-to-edge with the article text at all widths. Full npm run build passes (1097 pages).