fix(root): resize expanded code previews

[sylvesterkaczmarek]

Summary

Fix code preview height recalculation when users toggle Show full code and Show less code.

Problem

The code preview panels share an explicit synchronized height. After expanding a preview, reading scrollHeight while that larger fixed height is still applied can preserve the expanded height when the preview is collapsed again.

Fix

Temporarily reset both panel heights to auto before measuring their natural scrollHeight, then restore the synchronized height using the fresh measurement. This preserves equal-height framework tabs while allowing both expansion and collapse to resize correctly.

Verification

On the Date Picker code page, the first preview measures 58 px initially, expands to 666 px, and returns to 58 px after Show less code. Prettier, TypeScript, ESLint, Jest, and the full production build pass locally.

Closes #1845

[GCHQ-Developer-530]

Please can you rebase this pull request?

[sylvesterkaczmarek]

Rebased onto the latest develop. Thanks!

[GCHQ-Developer-299]

When tested locally the change works, however when you minimise the code preview it does not return to the correct size:

Screen.Recording.2026-08-27.at.11.44.17.mov

However, this change does seem to remedy #1844 (i've not had the Code Previews fail to appear while testing these changes)

[sylvesterkaczmarek]

Thanks for catching the collapse case. I’ve rebased this onto the current develop and updated the height calculation so the panels are measured at their natural height before the shared height is reapplied. On the Date Picker example I verified 58 px → 666 px → 58 px across compact, full, and compact states. Prettier, TypeScript, ESLint, Jest, and the full production build all pass locally. Thanks again.