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/ClassSelector.cjs

@@ -0,0 +1,31 @@
+'use strict';
+
+const types = require('../../tokenizer/types.cjs');
+
+const FULLSTOP = 0x002E; // U+002E FULL STOP (.)
+
+// '.' ident
+const name = 'ClassSelector';
+const structure = {
+    name: String
+};
+
+function parse() {
+    this.eatDelim(FULLSTOP);
+
+    return {
+        type: 'ClassSelector',
+        loc: this.getLocation(this.tokenStart - 1, this.tokenEnd),
+        name: this.consume(types.Ident)
+    };
+}
+
+function generate(node) {
+    this.token(types.Delim, '.');
+    this.token(types.Ident, node.name);
+}
+
+exports.generate = generate;
+exports.name = name;
+exports.parse = parse;
+exports.structure = structure;