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/memfs/lib/encoding.js

@@ -0,0 +1,19 @@
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+exports.strToEncoding = exports.assertEncoding = exports.ENCODING_UTF8 = void 0;
+var buffer_1 = require("./internal/buffer");
+var errors = require("./internal/errors");
+exports.ENCODING_UTF8 = 'utf8';
+function assertEncoding(encoding) {
+    if (encoding && !buffer_1.Buffer.isEncoding(encoding))
+        throw new errors.TypeError('ERR_INVALID_OPT_VALUE_ENCODING', encoding);
+}
+exports.assertEncoding = assertEncoding;
+function strToEncoding(str, encoding) {
+    if (!encoding || encoding === exports.ENCODING_UTF8)
+        return str; // UTF-8
+    if (encoding === 'buffer')
+        return new buffer_1.Buffer(str); // `buffer` encoding
+    return new buffer_1.Buffer(str).toString(encoding); // Custom encoding
+}
+exports.strToEncoding = strToEncoding;