Improve tree not found page (#26570) (#27346)

Backport #26570 by @yp05327

Before:

![before](https://github.com/go-gitea/gitea/assets/18380374/383822d5-7d77-4ec3-b49b-4ab1e8b167ce)

After:

![after](https://github.com/go-gitea/gitea/assets/18380374/32afa0a3-fa05-4087-b96e-7d067f0ed756)

In Github:
https://github.com/yp05327/test/blob/main/test.drawio

Updated:
UI changed

![image](https://github.com/go-gitea/gitea/assets/18380374/41ed07ff-b815-4b4e-9779-5ab36b5f3980)

![image](https://github.com/go-gitea/gitea/assets/18380374/5d7b28d6-a2fc-4d4c-8d6d-d93f9c9a270b)

Co-authored-by: yp05327 <576951401@qq.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: delvh <dev.lh@web.de>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

options/locale/locale_en-US.ini

@@ -112,6 +112,7 @@ step2 = Step 2:
 
 error = Error
 error404 = The page you are trying to reach either <strong>does not exist</strong> or <strong>you are not authorized</strong> to view it.
+go_back = Go Back
 
 never = Never
 unknown = Unknown
@@ -1012,6 +1013,10 @@ blame.ignore_revs = Ignoring revisions in <a href="%s">.git-blame-ignore-revs</a
 blame.ignore_revs.failed = Failed to ignore revisions in <a href="%s">.git-blame-ignore-revs</a>.
 author_search_tooltip = Shows a maximum of 30 users
 
+tree_path_not_found_commit = Path %[1]s doesn't exist in commit %[2]s
+tree_path_not_found_branch = Path %[1]s doesn't exist in branch %[2]s
+tree_path_not_found_tag = Path %[1]s doesn't exist in tag %[2]s
+
 transfer.accept = Accept Transfer
 transfer.accept_desc =  Transfer to "%s"
 transfer.reject = Reject Transfer