fix(ranking): announce leaderboard loading to screen readers

The shared loading placeholder hid the dots from assistive tech and
left the status region empty. Add the existing common loading label
as visually hidden text.

src/components/analysis/ranking/sections/RankingLoadingBody.vue

@@ -1,9 +1,13 @@
 <script setup lang="ts">
+import { useI18n } from 'vue-i18n'
 import { LoadingDots } from '@/components/UI'
+
+const { t } = useI18n()
 </script>
 
 <template>
   <div class="flex h-56 items-center justify-center" role="status" aria-live="polite">
+    <span class="sr-only">{{ t('common.loading') }}</span>
     <LoadingDots />
   </div>
 </template>