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/issue/sidebar/due_date.tmpl

@@ -2,7 +2,7 @@
 <span class="text"><strong>{{ctx.Locale.Tr "repo.issues.due_date"}}</strong></span>
 <div class="ui form tw-mt-2">
 	{{if .Issue.DeadlineUnix}}
-		<div class="tw-flex tw-justify-between tw-items-center tw-gap-2">
+		<div class="flex-left-right">
 			<div class="due-date {{if .Issue.IsOverdue}}tw-text-red{{end}}" {{if .Issue.IsOverdue}}data-tooltip-content="{{ctx.Locale.Tr "repo.issues.due_date_overdue"}}"{{end}}>
 				{{svg "octicon-calendar"}} {{DateUtils.AbsoluteLong .Issue.DeadlineUnix}}
 			</div>