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/view_content/attachments.tmpl

@@ -19,7 +19,7 @@
 				</a>
 			</div>
 			<div class="tw-p-2 tw-flex tw-items-center">
-				<span class="ui text grey">{{.Size | FileSize}}</span>
+				<span class="ui tw-text-text-light">{{.Size | FileSize}}</span>
 			</div>
 		</div>
 	{{end -}}