feat: enhance layout and styling of content rows and header

- Updated content card width from 140/180px to 200/280px for improved visibility
- Changed image class to use 'object-contain' and added background color for better aesthetics
- Introduced a gradient background for the header with dynamic styles based on scroll position
- Added new CSS classes for header gradient effects and improved backdrop filter for a modern look

Co-authored-by: Cursor <cursoragent@cursor.com>

src/components/ContentRow.vue

@@ -25,13 +25,13 @@
         <div
           v-for="content in contents"
           :key="content.id"
-          class="content-card flex-shrink-0 w-[140px] md:w-[180px]"
+          class="content-card flex-shrink-0 w-[200px] md:w-[280px]"
           @click="$emit('content-click', content)"
         >
           <img 
             :src="content.thumbnail" 
             :alt="content.title"
-            class="w-full aspect-[2/3] object-cover rounded-lg"
+            class="w-full aspect-[2/3] object-contain rounded-lg bg-neutral-900"
             loading="lazy"
           />
           <div class="mt-2">