feat: update video content and improve grid layout

- Add new video thumbnails for music, game, tech, and art categories
- Update video data with more realistic content
- Adjust grid layout dimensions for better responsiveness
- Simplify category buttons in the UI
- Remove unused maxresdefault.jpg cover image

css/style.css

@@ -304,7 +304,7 @@ body {
 /* 视频网格 */
 .video-grid {
     display: grid;
-    grid-template-columns: repeat(auto-fill, minmax(360px, 1fr));
+    grid-template-columns: repeat(auto-fill, minmax(380px, 1fr));
     gap: 24px;
     margin-bottom: 48px;
 }
@@ -474,7 +474,7 @@ body {
 
 .shorts-grid {
     display: grid;
-    grid-template-columns: repeat(auto-fill, minmax(180px, 1fr));
+    grid-template-columns: repeat(auto-fill, minmax(160px, 1fr));
     gap: 16px;
 }