fix: prevent asset conflicts between React and Grid.js versions

Add coexistence checks to all enqueue methods to prevent loading
both React and Grid.js assets simultaneously.

Changes:
- ReactAdmin.php: Only enqueue React assets when ?react=1
- Init.php: Skip Grid.js when React active on admin pages
- Form.php, Coupon.php, Access.php: Restore classic assets when ?react=0
- Customer.php, Product.php, License.php: Add coexistence checks

Now the toggle between Classic and React versions works correctly.

Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

node_modules/loader-utils/lib/parseString.js

@@ -0,0 +1,23 @@
+'use strict';
+
+function parseString(str) {
+  try {
+    if (str[0] === '"') {
+      return JSON.parse(str);
+    }
+
+    if (str[0] === "'" && str.substr(str.length - 1) === "'") {
+      return parseString(
+        str
+          .replace(/\\.|"/g, (x) => (x === '"' ? '\\"' : x))
+          .replace(/^'|'$/g, '"')
+      );
+    }
+
+    return JSON.parse('"' + str + '"');
+  } catch (e) {
+    return str;
+  }
+}
+
+module.exports = parseString;