fix(dashboard): use secondary variant for customize design button (#816)

Change the Customize design button on the certificate design page from
primary to secondary styling for better visual hierarchy.

Co-authored-by: Cursor Agent <cursoragent@cursor.com>
Co-authored-by: Rotimi Best <rotimi-best@users.noreply.github.com>

apps/dashboard/src/lib/features/course/components/ceritficate/certificate-design.svelte

@@ -113,7 +113,7 @@
         </div>
       </Card.Content>
       <Card.Footer>
-        <Button class="w-full justify-center" disabled={$isFreePlan || !courseId} href={editorHref}>
+        <Button variant="secondary" class="w-full justify-center" disabled={$isFreePlan || !courseId} href={editorHref}>
           {#if $isFreePlan}
             <ZapIcon class="size-4" />
           {/if}