don't path-encode ref name #4698

Example:

https://tangled.org/tangled.org/core/tree/sl%2Fweb%2Fpr-comments/blog/posts

It should rather be:

https://tangled.org/tangled.org/core/tree/sl/web/pr-comments/blog/posts

We can do fast branch/tag-name lookup without even help of knotmirror since org.tangled.git.refs/self holds packed-refs content. We can ask for it on repo page load against bobbin.