docs: fix docsify sidebar links

[DeoJin]

Summary

• switch docs/docsify/sidebar.md from root-relative links to file-relative links so the sidebar works when viewed directly on GitHub
• fix the SOCKS5 sidebar entry to point at the existing Socks5ProxyAgent.md page

Validation

• powershell link check to verify every sidebar target resolves on disk

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.89%. Comparing base (1c5dc1a) to head (b424cf3).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4906      +/-   ##
==========================================
- Coverage   92.90%   92.89%   -0.01%     
==========================================
  Files         112      112              
  Lines       35638    35638              
==========================================
- Hits        33108    33107       -1     
- Misses       2530     2531       +1     

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[mcollina]

have you verified this work in docsify too?