fix: correct Windows localized date encoding

[OrzMiku]

Summary

This PR fixes localized date formatting on Windows when the time locale uses a non-UTF-8 code page.

Related Issues

Related #

Closes #

Changes

• Temporarily formats dates with a UTF-8 LC_TIME locale on Windows
• Routes date string formatting through the shared os_date() helper

Before	After

Checklist

I confirm that I have:

• Followed the
  Conventional Commits
  specification (e.g., feat: add new feature, fix: correct bug,
  docs: update documentation).
• My PR title also follows the conventional commits specification.
• Updated relevant documentation, if necessary.
• Thoroughly tested my changes.
• Added tests (if applicable) and verified existing tests pass with
  make test.
• Checked for breaking changes and documented them, if any.

[kristijanhusak]

Thanks!