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/_escapeHtmlChar.js

@@ -0,0 +1,21 @@
+var basePropertyOf = require('./_basePropertyOf');
+
+/** Used to map characters to HTML entities. */
+var htmlEscapes = {
+  '&': '&',
+  '<': '&lt;',
+  '>': '&gt;',
+  '"': '&quot;',
+  "'": '&#39;'
+};
+
+/**
+ * Used by `_.escape` to convert characters to HTML entities.
+ *
+ * @private
+ * @param {string} chr The matched character to escape.
+ * @returns {string} Returns the escaped character.
+ */
+var escapeHtmlChar = basePropertyOf(htmlEscapes);
+
+module.exports = escapeHtmlChar;