feat: improve LMS course discovery and enrollment UX

- Add paginated recommended courses to LMS dashboard (top 3, list
    view)
    and explore page (12 per page); exclude courses blocking new
    students
  - Polish course preview modal: remove padding, render requirements as
    HTML, round banner image, secondary close button
  - Redirect to course start page after successful enrollment instead of
    /lms;
    keep spinner active until navigation completes
  - Auto-enable "allow new students" when a course is published
  - Move Explore after My Learning in LMS sidebar nav
  - Move Certificates after Content in course sidebar
  - Add hiddenColumns prop to CourseListRow; show "Learn more" button
    instead of actions menu in LMS explore context

apps/dashboard/src/routes/(org-site)/course/[slug]/enroll/+page.svelte

@@ -75,6 +75,8 @@
       return;
     }
 
+    let navigatingAway = false;
+
     try {
       const body = data.token ? { inviteToken: data.token } : {};
       const result = await courseApi.enroll(data.course!.id, body);
@@ -90,10 +92,11 @@
         already_joined: result.data.alreadyJoined
       });
 
+      navigatingAway = true;
       // need to force page reload to avoid cache issues
       window.location.href = result.data.redirectTo || '/lms';
     } finally {
-      loading = false;
+      if (!navigatingAway) loading = false;
     }
   }