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/ajv/lib/compile/error_classes.js

@@ -0,0 +1,34 @@
+'use strict';
+
+var resolve = require('./resolve');
+
+module.exports = {
+  Validation: errorSubclass(ValidationError),
+  MissingRef: errorSubclass(MissingRefError)
+};
+
+
+function ValidationError(errors) {
+  this.message = 'validation failed';
+  this.errors = errors;
+  this.ajv = this.validation = true;
+}
+
+
+MissingRefError.message = function (baseId, ref) {
+  return 'can\'t resolve reference ' + ref + ' from id ' + baseId;
+};
+
+
+function MissingRefError(baseId, ref, message) {
+  this.message = message || MissingRefError.message(baseId, ref);
+  this.missingRef = resolve.url(baseId, ref);
+  this.missingSchema = resolve.normalizeId(resolve.fullPath(this.missingRef));
+}
+
+
+function errorSubclass(Subclass) {
+  Subclass.prototype = Object.create(Error.prototype);
+  Subclass.prototype.constructor = Subclass;
+  return Subclass;
+}