fix: use standard max-width media query syntax in admin-styles.css (issue #43) (#68)

Replace invalid CSS media-feature range notation with universally-supported
traditional syntax for better browser compatibility.

- admin/css/admin-styles.css:127: (width <= 782px) → (max-width: 782px)

admin/css/admin-styles.css

@@ -124,7 +124,7 @@
 }
 
 /* Responsive Styles */
-@media screen and (width <= 782px) {
+@media screen and (max-width: 782px) {
     .wpst-form-table th {
         width: 100%;
         display: block;