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/diff/compare.tmpl

@@ -46,12 +46,12 @@
 						<div class="ui grid">
 							<div class="two column row">
 								<a class="reference column" href="#" data-target=".base-branch-list">
-									<span class="text black">
+									<span class="tw-text-text">
 										{{svg "octicon-git-branch"}} {{ctx.Locale.Tr "repo.branches"}}
 									</span>
 								</a>
 								<a class="reference column" href="#" data-target=".base-tag-list">
-									<span class="text black">
+									<span class="tw-text-text">
 										{{svg "octicon-tag"}} {{ctx.Locale.Tr "repo.tags"}}
 									</span>
 								</a>
@@ -117,12 +117,12 @@
 						<div class="ui grid">
 							<div class="two column row">
 								<a class="reference column" href="#" data-target=".head-branch-list">
-									<span class="text black">
+									<span class="tw-text-text">
 										{{svg "octicon-git-branch"}} {{ctx.Locale.Tr "repo.branches"}}
 									</span>
 								</a>
 								<a class="reference column" href="#" data-target=".head-tag-list">
-									<span class="text black">
+									<span class="tw-text-text">
 										{{svg "octicon-tag"}} {{ctx.Locale.Tr "repo.tags"}}
 									</span>
 								</a>