feat(lms): add student certificates page and sidebar nav (#696)

* feat(lms): add student certificates page and sidebar nav

Add a Certificates item to the student LMS sidebar that lists courses
where the student has earned a certificate. Each course card includes a
View Certificate action linking to the existing per-course certificate
page.

* refactor: reuse isOrgOnFreePlan helper from org store

* chore(i18n): add certificates translations for all locales

---------

apps/dashboard/src/routes/(app)/lms/certificates/+page.svelte

@@ -0,0 +1,23 @@
+<script lang="ts">
+  import { CertificatesPage } from '$features/lms/pages';
+  import { t } from '$lib/utils/functions/translations';
+  import * as Page from '@cio/ui/base/page';
+</script>
+
+<svelte:head>
+  <title>Certificates - ClassroomIO</title>
+</svelte:head>
+
+<Page.Root class="w-full">
+  <Page.Header>
+    <Page.HeaderContent>
+      <Page.Title>{$t('certificates.heading')}</Page.Title>
+      <Page.Subtitle>{$t('certificates.description')}</Page.Subtitle>
+    </Page.HeaderContent>
+  </Page.Header>
+  <Page.Body>
+    {#snippet child()}
+      <CertificatesPage />
+    {/snippet}
+  </Page.Body>
+</Page.Root>