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/comments.tmpl

@@ -13,11 +13,11 @@
 		<div class="comment-header avatar-content-left-arrow">
 			<div class="comment-header-left">
 				{{if .OriginalAuthor}}
-					<span class="text black tw-font-semibold tw-mr-1">
+					<span class="tw-text-text tw-font-semibold tw-mr-1">
 						{{svg (MigrationIcon $.root.Repository.GetOriginalURLHostname)}}
 						{{.OriginalAuthor}}
 					</span>
-					<span class="text grey muted-links">
+					<span class="tw-text-text-light muted-links">
 						{{ctx.Locale.Tr "repo.issues.commented_at" .HashTag $createdStr}}
 					</span>
 					<span class="text migrate">
@@ -26,7 +26,7 @@
 						{{end}}
 					</span>
 				{{else}}
-					<span class="text grey muted-links">
+					<span class="tw-text-text-light muted-links">
 						{{template "shared/user/namelink" .Poster}}
 						{{ctx.Locale.Tr "repo.issues.commented_at" .HashTag $createdStr}}
 					</span>