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/css-tree/cjs/syntax/node/CDO.cjs

@@ -0,0 +1,26 @@
+'use strict';
+
+const types = require('../../tokenizer/types.cjs');
+
+const name = 'CDO';
+const structure = [];
+
+function parse() {
+    const start = this.tokenStart;
+
+    this.eat(types.CDO); // <!--
+
+    return {
+        type: 'CDO',
+        loc: this.getLocation(start, this.tokenStart)
+    };
+}
+
+function generate() {
+    this.token(types.CDO, '<!--');
+}
+
+exports.generate = generate;
+exports.name = name;
+exports.parse = parse;
+exports.structure = structure;