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/core-js/es/json/index.js

@@ -0,0 +1,14 @@
+'use strict';
+require('../../modules/es.object.create');
+require('../../modules/es.object.freeze');
+require('../../modules/es.object.keys');
+require('../../modules/es.date.to-json');
+require('../../modules/es.json.is-raw-json');
+require('../../modules/es.json.parse');
+require('../../modules/es.json.raw-json');
+require('../../modules/es.json.stringify');
+require('../../modules/es.json.to-string-tag');
+var path = require('../../internals/path');
+
+// eslint-disable-next-line es/no-json -- safe
+module.exports = path.JSON || (path.JSON = { stringify: JSON.stringify });

node_modules/core-js/es/json/is-raw-json.js

@@ -0,0 +1,5 @@
+'use strict';
+require('../../modules/es.json.is-raw-json');
+var path = require('../../internals/path');
+
+module.exports = path.JSON.isRawJSON;

node_modules/core-js/es/json/parse.js

@@ -0,0 +1,6 @@
+'use strict';
+require('../../modules/es.object.keys');
+require('../../modules/es.json.parse');
+var path = require('../../internals/path');
+
+module.exports = path.JSON.parse;

node_modules/core-js/es/json/raw-json.js

@@ -0,0 +1,7 @@
+'use strict';
+require('../../modules/es.object.create');
+require('../../modules/es.object.freeze');
+require('../../modules/es.json.raw-json');
+var path = require('../../internals/path');
+
+module.exports = path.JSON.rawJSON;

node_modules/core-js/es/json/stringify.js

@@ -0,0 +1,13 @@
+'use strict';
+require('../../modules/es.date.to-json');
+require('../../modules/es.json.stringify');
+var path = require('../../internals/path');
+var apply = require('../../internals/function-apply');
+
+// eslint-disable-next-line es/no-json -- safe
+if (!path.JSON) path.JSON = { stringify: JSON.stringify };
+
+// eslint-disable-next-line no-unused-vars -- required for `.length`
+module.exports = function stringify(it, replacer, space) {
+  return apply(path.JSON.stringify, null, arguments);
+};

node_modules/core-js/es/json/to-string-tag.js

@@ -0,0 +1,4 @@
+'use strict';
+require('../../modules/es.json.to-string-tag');
+
+module.exports = 'JSON';