fix(a11y): wrap SidebarItem with <li> in SidebarGroup

[72umesh]

Description

This PR fixes an accessibility issue in the Sidebar navigation.
Currently, sidebar items are placed directly inside <ul> without <li> wrappers, which breaks HTML list rules and causes accessibility errors.

Validation

Before the fix (invalid – direct <a> inside <ul>):

After the fix (correct – wrapped in <li>):

Related Issues

#8465

Check List

• I have read the Contributing Guidelines and made commit messages that follow the guideline.
• I have run pnpm format to ensure the code follows the style guide.
• I have run pnpm test to check if all tests are passing.
• I have run pnpm build to check if the website builds without errors.
• I've covered new added functionality with unit tests if necessary.

[vercel]

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Project	Deployment	Review	Updated (UTC)
nodejs-org	Ready	Preview	Jan 4, 2026 3:25am

[github-actions]

👋 Codeowner Review Request

The following codeowners have been identified for the changed files:

Team reviewers: @nodejs/nodejs-website

Please review the changes when you have a chance. Thank you! 🙏

[ovflowd]

SGTM

[github-actions]

Lighthouse Results

URL	Performance	Accessibility	Best Practices	SEO	Report
/en	🟢 98	🟢 96	🟢 100	🟢 100	🔗
/en/about	🟢 99	🟢 97	🟢 100	🟠 88	🔗
/en/about/previous-releases	🟢 98	🟢 100	🟢 100	🟢 100	🔗
/en/download	🟢 97	🟢 100	🟢 100	🟢 100	🔗
/en/download/archive/current	🟢 100	🟢 100	🟢 100	🟢 100	🔗
/en/blog	🟢 100	🟢 100	🟢 96	🟢 100	🔗

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 74.24%. Comparing base (fcfc7e2) to head (0aceb3b).
⚠️ Report is 4 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8515      +/-   ##
==========================================
+ Coverage   74.21%   74.24%   +0.03%     
==========================================
  Files         106      106              
  Lines        9102     9102              
  Branches      308      307       -1     
==========================================
+ Hits         6755     6758       +3     
+ Misses       2345     2342       -3     
  Partials        2        2              

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