Fix N+1 query on homepage for recent courses (#357)

Add select_related("course") to the recent_views queryset to prevent
multiple database queries when accessing course objects. This resolves
the performance issue where a separate query was executed for each
CourseUserView when building the recent_courses list.

Fixes DOCHUB-21Y

Co-authored-by: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: C4ptainCrunch

www/views.py

@@ -22,9 +22,11 @@ def index(request):
             .prefetch_related("tags")
             .order_by("-created")[:ndocs]
         )
-        recent_views = CourseUserView.objects.filter(user=request.user).order_by(
-            "-last_view"
-        )[:5]
+        recent_views = (
+            CourseUserView.objects.filter(user=request.user)
+            .select_related("course")
+            .order_by("-last_view")[:5]
+        )
         recent_courses = [x.course for x in recent_views]
         context = {
             "search": SearchForm(),