Use light background for card images

Replaces the high-contrast black (#1a1a1a) with a soft
light gray (#f0f4f8) in light mode and muted dark (#21262d)
in dark mode.

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

Author: robertogl

index.html

@@ -192,12 +192,16 @@
             width: 100%;
             aspect-ratio: 16 / 9;
             overflow: hidden;
-            background: #1a1a1a;
+            background: #f0f4f8;
             display: flex;
             align-items: center;
             justify-content: center;
         }
 
+        [data-theme="dark"] .card-image {
+            background: #21262d;
+        }
+
         .card-image img {
             width: 100%;
             height: 100%;