fix: Fix URL encoding for refs containing special characters

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What does this MR do and why?

Fix 404 error when clicking tags with special characters in MR page

Users encounter 404 errors when clicking on tags that contain special characters (such as "C#") from Merge Request pages
Root cause: The refs_list.vue file doesn't properly encode the ref parameter in the URL construction

References

Screenshots or screen recordings

6e7f1be2d9aab5bf508f6de32207c0a3

How to set up and validate locally

1. Create a project with commits
2. Create a tag with special characters (e.g. "C#")
3. View commit details in MR page
4. Click the tag - results in 404

MR acceptance checklist

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