Refactor frontend tw-justify-between layouts to flex-left-right (#37291)

This PR standardizes left/right two-child frontend layouts on
`flex-left-right` and removes ad-hoc `tw-justify-between` combinations.
The goal is consistent wrapping + spacing behavior under narrow widths
with less utility-class churn.

Also: remove useless "flex-center-wrap", slightly improve some templates
(no visual change, tested)

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: wxiaoguang <2114189+wxiaoguang@users.noreply.github.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

templates/repo/diff/box.tmpl

@@ -211,7 +211,7 @@
 
 				{{if .Diff.IsIncomplete}}
 					<div class="diff-file-box file-content tw-mt-2" id="diff-incomplete">
-						<h4 class="ui top attached header tw-font-normal tw-flex tw-items-center tw-justify-between">
+						<h4 class="ui top attached header tw-font-normal flex-left-right">
 							{{ctx.Locale.Tr "repo.diff.too_many_files"}}
 							<a class="ui basic tiny button" id="diff-show-more-files" data-href="?skip-to={{.Diff.End}}&file-only=true">{{ctx.Locale.Tr "repo.diff.show_more"}}</a>
 						</h4>