fix(ui): keep pause form description visible

[Bortlesboat]

closes #21491

This PR keeps pause/resume input guidance visible while long schema forms scroll.

Details

The markdown description and schema form currently share one overflow-y-auto container. With enough fields, scrolling the form also removes validation context such as "One or more of your inputs were invalid" from view.

The description is now a non-shrinking sibling above the scroll region, and only the schema form scrolls. Dialog headers, footers, schema behavior, and API behavior are unchanged.

The existing ten-field regression now asserts both sides of the layout contract: the description is outside the scroll container and the final field remains inside it.

Verification:

• npm test -- resume-flow-run-dialog.test.tsx --run (9 passed)
• Biome check on both touched files
• ESLint on both touched files
• npm run build
• git diff --check

The local Node version was 24.14.0 versus the package's declared Node 22 range; tests and the full production build still completed successfully.

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[desertaxle]

Could we make the description area shrink on shorter viewports? With a long description it pushes the form and the Resume/Cancel buttons below the screen. I think we should preserve the separate scrolling behavior while ensuring the footer always stays accessible, ideally with a small-viewport test to cover it.