fix(course): preserve cover image aspect ratio in settings preview

The preview forced images into a 280x200 box with default object-fit,
squeezing non-matching aspect ratios. Use object-cover so the image
fills the frame at its true aspect ratio and crops overflow instead.

apps/dashboard/src/lib/features/course/pages/settings.svelte

@@ -369,10 +369,9 @@
       <Field.Field>
         <div class="relative w-fit">
           <img
-            style="min-width:280px; min-height:200px"
             alt="Course cover"
             src={$settings.logo ? $settings.logo : '/images/classroomio-course-img-template.jpg'}
-            class="relative mt-2 h-[200px] w-[280px] rounded-md md:mt-0"
+            class="relative mt-2 h-[200px] w-[280px] rounded-md border object-cover md:mt-0"
           />
         </div>
       </Field.Field>