fix: remove hero banners, fix theme tokens, align course card stats

- Remove dark gradient hero sections from Courses and Olympiads pages
- Move search input inline with tab filters
- Fix StudentProfile scoped styles to use Frappe UI CSS variables
  instead of hardcoded hex colors (fixes white/dark theme compatibility)
- Fix CourseCard stats row jumping by adding min-height to description
  and stats container

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/components/CourseCard.vue

@@ -75,13 +75,13 @@
 				{{ course.title }}
 			</div>
 
-			<!-- Short intro -->
-			<p class="text-xs text-ink-gray-5 leading-relaxed line-clamp-2 mb-3 mt-0.5">
+			<!-- Short intro: fixed 2-line height so cards stay aligned -->
+			<p class="text-xs text-ink-gray-5 leading-relaxed line-clamp-2 mb-3 mt-0.5" style="min-height: 2.5rem">
 				{{ course.short_introduction }}
 			</p>
 
-			<!-- Stats row -->
-			<div class="flex items-center gap-3 text-xs text-ink-gray-5 mb-3 flex-wrap">
+			<!-- Stats row: always occupies space even when empty -->
+			<div class="flex items-center gap-3 text-xs text-ink-gray-5 mb-3 flex-wrap" style="min-height: 1.25rem">
 				<span v-if="course.lessons" class="flex items-center gap-1">
 					<BookOpen class="h-3.5 w-3.5" />
 					{{ course.lessons }} {{ __('lessons') }}