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/lodash/_createMathOperation.js

@@ -0,0 +1,38 @@
+var baseToNumber = require('./_baseToNumber'),
+    baseToString = require('./_baseToString');
+
+/**
+ * Creates a function that performs a mathematical operation on two values.
+ *
+ * @private
+ * @param {Function} operator The function to perform the operation.
+ * @param {number} [defaultValue] The value used for `undefined` arguments.
+ * @returns {Function} Returns the new mathematical operation function.
+ */
+function createMathOperation(operator, defaultValue) {
+  return function(value, other) {
+    var result;
+    if (value === undefined && other === undefined) {
+      return defaultValue;
+    }
+    if (value !== undefined) {
+      result = value;
+    }
+    if (other !== undefined) {
+      if (result === undefined) {
+        return other;
+      }
+      if (typeof value == 'string' || typeof other == 'string') {
+        value = baseToString(value);
+        other = baseToString(other);
+      } else {
+        value = baseToNumber(value);
+        other = baseToNumber(other);
+      }
+      result = operator(value, other);
+    }
+    return result;
+  };
+}
+
+module.exports = createMathOperation;