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/cssstyle/lib/properties/backgroundRepeat.js

@@ -0,0 +1,32 @@
+'use strict';
+
+var parsers = require('../parsers');
+
+var parse = function parse(v) {
+  if (
+    parsers.valueType(v) === parsers.TYPES.KEYWORD &&
+    (v.toLowerCase() === 'repeat' ||
+      v.toLowerCase() === 'repeat-x' ||
+      v.toLowerCase() === 'repeat-y' ||
+      v.toLowerCase() === 'no-repeat' ||
+      v.toLowerCase() === 'inherit')
+  ) {
+    return v;
+  }
+  return undefined;
+};
+
+module.exports.isValid = function isValid(v) {
+  return parse(v) !== undefined;
+};
+
+module.exports.definition = {
+  set: function(v) {
+    this._setProperty('background-repeat', parse(v));
+  },
+  get: function() {
+    return this.getPropertyValue('background-repeat');
+  },
+  enumerable: true,
+  configurable: true,
+};