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/editor/edit.tmpl

@@ -18,7 +18,7 @@
 					{{if not .NotEditableReason}}
 						<div class="field">
 							<div class="ui top attached header">
-								<div class="flex-text-block tw-justify-between tw-flex-wrap">
+								<div class="flex-left-right">
 									<div class="ui compact small menu small-menu-items repo-editor-menu" data-repo-link="{{.RepoLink}}" data-ref-sub-url="{{.RefTypeNameSubURL}}" data-branch-name="{{.BranchName}}">
 										<a class="active item" data-tab="write">{{svg "octicon-code"}} {{if .IsNewFile}}{{ctx.Locale.Tr "repo.editor.new_file"}}{{else}}{{ctx.Locale.Tr "repo.editor.edit_file"}}{{end}}</a>
 										<a class="item {{if not .CodeEditorConfig.Previewable}}tw-hidden{{end}}" data-tab="preview">{{svg "octicon-eye"}} {{ctx.Locale.Tr "preview"}}</a>