fix: partial revert of 18cd69

[avivkeller]

Fixes: #9012

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[cursor]

PR Summary

Low Risk
Single CSS change in the article container with no auth, data, or API impact; layout-only fix with localized visual/scroll behavior.

Overview
Reverts part of the article layout sidebar sticky styling so the first column again uses top-0 and h-svh instead of offsetting below --header-height and using calc(100svh - var(--header-height)).

This partial rollback of commit 18cd69 restores the previous full-viewport sticky sidebar behavior on medium+ breakpoints, addressing nodejs.org#9012.

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Project	Deployment	Actions	Updated (UTC)
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[avivkeller]

@bmuenzenmeyer can you set up changesets in this repo + require changes to ui-components to have a changeset?

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.59%. Comparing base (61cd932) to head (9e57ea2).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9013      +/-   ##
==========================================
+ Coverage   74.58%   74.59%   +0.01%     
==========================================
  Files         100      100              
  Lines        8801     8801              
  Branches      324      324              
==========================================
+ Hits         6564     6565       +1     
+ Misses       2233     2232       -1     
  Partials        4        4              

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📦 Build Size Comparison

Summary

Metric	Value
Old Total First Load JS	10.70 MB
New Total First Load JS	10.70 MB
Delta	0 B (0.00%)