Use same leaderboard display logic in dashboard as course page

Only show leaderboard button when course.first_homework_scored is True

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: alexeygrigorev

courses/templates/courses/dashboard.html

@@ -14,9 +14,11 @@ <h1 class="mb-4">
 
 <!-- Navigation Links -->
 <div class="mb-4">
+  {% if course.first_homework_scored %}
   <a href="{% url 'leaderboard' course.slug %}" class="btn btn-primary">
     <i class="fas fa-trophy"></i> View Leaderboard
   </a>
+  {% endif %}
 </div>
 
 <!-- Total Enrollment -->