[rustatian]

Reason for This PR

Migrate the file server to Fiber v3 using the official migration guide.

Description of Changes

• Update Fiber to v3.6.1 and use its static middleware and listener options.
• Decode URL paths for static file lookup and match prefixes at path-segment boundaries.

License Acceptance

By submitting this pull request, I confirm that my contribution is made under the terms of the MIT license.

PR Checklist

• All commits in this PR are signed.
• The reason for this PR is clear.
• The description covers the changes.
• Any required documentation changes are included.
• Changelog entry: not applicable; this repository has no CHANGELOG.md.
• All added or changed functionality is tested.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.14%. Comparing base (485bed4) to head (2880a45).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #107      +/-   ##
==========================================
+ Coverage   82.85%   87.14%   +4.28%     
==========================================
  Files           2        2              
  Lines          70       70              
==========================================
+ Hits           58       61       +3     
+ Misses         12        9       -3     

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