Improve mode card icon spacing and centering

- Increase margin-bottom from 6px to 12px for better spacing
- Add flexbox centering to properly align icons
- Bump icon size to 28px for better visual balance

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

static/css/index.css

@@ -340,14 +340,16 @@ body {
 }
 
 .mode-card .mode-icon {
-    font-size: 1.5rem;
-    margin-bottom: 6px;
+    display: flex;
+    justify-content: center;
+    align-items: center;
+    margin-bottom: 12px;
     color: var(--text-secondary);
 }
 
 .mode-card .mode-icon svg {
-    width: 24px;
-    height: 24px;
+    width: 28px;
+    height: 28px;
 }
 
 .mode-card .mode-name {