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/branch/list.tmpl

@@ -70,7 +70,7 @@
 			</div>
 		{{end}}
 
-		<h4 class="ui top attached header tw-flex tw-items-center tw-justify-between">
+		<h4 class="ui top attached header">
 			<div class="flex-text-block">
 				{{ctx.Locale.Tr "repo.branches"}}
 			</div>