Refactor text utility classes to Tailwind CSS (#36703)

Replace Fomantic/custom CSS text utility classes with their Tailwind
equivalents:

- `.text.<color>` compound classes → `tw-text-<color>` classes
- `.text.small` (`font-size: 0.75em`) → `tw-text-xs` (11px)
- `.text.truncate` (`overflow-x: hidden; text-overflow: ellipsis;
white-space: nowrap; display: inline-block`) → `tw-inline-block
tw-truncate`

Remove the now-unused CSS rules from `base.css` and `dashboard.css`.

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

templates/repo/issue/sidebar/due_date.tmpl

@@ -3,7 +3,7 @@
 <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="due-date {{if .Issue.IsOverdue}}text red{{end}}" {{if .Issue.IsOverdue}}data-tooltip-content="{{ctx.Locale.Tr "repo.issues.due_date_overdue"}}"{{end}}>
+			<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>
 			<div class="flex-text-block">