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/parser/sequence.js

@@ -0,0 +1,43 @@
+import { WhiteSpace, Comment } from '../tokenizer/index.js';
+
+export function readSequence(recognizer) {
+    const children = this.createList();
+    let space = false;
+    const context = {
+        recognizer
+    };
+
+    while (!this.eof) {
+        switch (this.tokenType) {
+            case Comment:
+                this.next();
+                continue;
+
+            case WhiteSpace:
+                space = true;
+                this.next();
+                continue;
+        }
+
+        let child = recognizer.getNode.call(this, context);
+
+        if (child === undefined) {
+            break;
+        }
+
+        if (space) {
+            if (recognizer.onWhiteSpace) {
+                recognizer.onWhiteSpace.call(this, child, children, context);
+            }
+            space = false;
+        }
+
+        children.push(child);
+    }
+
+    if (space && recognizer.onWhiteSpace) {
+        recognizer.onWhiteSpace.call(this, null, children, context);
+    }
+
+    return children;
+};