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-pure/modules/es.math.f16round.js

@@ -0,0 +1,15 @@
+'use strict';
+var $ = require('../internals/export');
+var floatRound = require('../internals/math-float-round');
+
+var FLOAT16_EPSILON = 0.0009765625;
+var FLOAT16_MAX_VALUE = 65504;
+var FLOAT16_MIN_VALUE = 6.103515625e-05;
+
+// `Math.f16round` method
+// https://tc39.es/ecma262/#sec-math.f16round
+$({ target: 'Math', stat: true }, {
+  f16round: function f16round(x) {
+    return floatRound(x, FLOAT16_EPSILON, FLOAT16_MAX_VALUE, FLOAT16_MIN_VALUE);
+  }
+});