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/@babel/runtime/regenerator/index.js

@@ -0,0 +1,15 @@
+// TODO(Babel 8): Remove this file.
+
+var runtime = require("../helpers/regeneratorRuntime")();
+module.exports = runtime;
+
+// Copied from https://github.com/facebook/regenerator/blob/main/packages/runtime/runtime.js#L736=
+try {
+  regeneratorRuntime = runtime;
+} catch (accidentalStrictMode) {
+  if (typeof globalThis === "object") {
+    globalThis.regeneratorRuntime = runtime;
+  } else {
+    Function("r", "regeneratorRuntime = r")(runtime);
+  }
+}