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/regenerator-runtime/runtime-module.js

@@ -0,0 +1,31 @@
+// This method of obtaining a reference to the global object needs to be
+// kept identical to the way it is obtained in runtime.js
+var g =
+  typeof global === "object" ? global :
+  typeof window === "object" ? window :
+  typeof self === "object" ? self : this;
+
+// Use `getOwnPropertyNames` because not all browsers support calling
+// `hasOwnProperty` on the global `self` object in a worker. See #183.
+var hadRuntime = g.regeneratorRuntime &&
+  Object.getOwnPropertyNames(g).indexOf("regeneratorRuntime") >= 0;
+
+// Save the old regeneratorRuntime in case it needs to be restored later.
+var oldRuntime = hadRuntime && g.regeneratorRuntime;
+
+// Force reevalutation of runtime.js.
+g.regeneratorRuntime = undefined;
+
+module.exports = require("./runtime");
+
+if (hadRuntime) {
+  // Restore the original runtime.
+  g.regeneratorRuntime = oldRuntime;
+} else {
+  // Remove the global property added by runtime.js.
+  try {
+    delete g.regeneratorRuntime;
+  } catch(e) {
+    g.regeneratorRuntime = undefined;
+  }
+}