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/webpack-dev-server/client/utils/getCurrentScriptSource.js

@@ -0,0 +1,24 @@
+/**
+ * @returns {string}
+ */
+function getCurrentScriptSource() {
+  // `document.currentScript` is the most accurate way to find the current script,
+  // but is not supported in all browsers.
+  if (document.currentScript) {
+    return document.currentScript.getAttribute("src");
+  }
+
+  // Fallback to getting all scripts running in the document.
+  var scriptElements = document.scripts || [];
+  var scriptElementsWithSrc = Array.prototype.filter.call(scriptElements, function (element) {
+    return element.getAttribute("src");
+  });
+  if (scriptElementsWithSrc.length > 0) {
+    var currentScript = scriptElementsWithSrc[scriptElementsWithSrc.length - 1];
+    return currentScript.getAttribute("src");
+  }
+
+  // Fail as there was no script to use.
+  throw new Error("[webpack-dev-server] Failed to get current script source.");
+}
+export default getCurrentScriptSource;