feat(ui): make IconButton square and mobile-tappable (44px min)

src/components/IconButton.tsx

@@ -17,7 +17,7 @@ const IconButton: React.FC<IconButtonProps> = ({
   title,
   ariaLabel,
   variant = 'ghost',
-  size = 28
+  size = 44
 }) => {
   return (
     <button

src/index.css

@@ -179,6 +179,8 @@ body {
   background: #2a2a2a;
   color: #ddd;
   cursor: pointer;
+  min-width: 44px; /* mobile tap target */
+  min-height: 44px; /* mobile tap target */
 }
 
 .icon-button:hover { background: #333; }