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/lib/syntax/node/WhiteSpace.js

@@ -0,0 +1,27 @@
+import { WhiteSpace } from '../../tokenizer/index.js';
+
+const SPACE = Object.freeze({
+    type: 'WhiteSpace',
+    loc: null,
+    value: ' '
+});
+
+export const name = 'WhiteSpace';
+export const structure = {
+    value: String
+};
+
+export function parse() {
+    this.eat(WhiteSpace);
+    return SPACE;
+
+    // return {
+    //     type: 'WhiteSpace',
+    //     loc: this.getLocation(this.tokenStart, this.tokenEnd),
+    //     value: this.consume(WHITESPACE)
+    // };
+}
+
+export function generate(node) {
+    this.token(WhiteSpace, node.value);
+}