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/rxjs/dist/esm/internal/BehaviorSubject.js

@@ -0,0 +1,27 @@
+import { Subject } from './Subject';
+export class BehaviorSubject extends Subject {
+    constructor(_value) {
+        super();
+        this._value = _value;
+    }
+    get value() {
+        return this.getValue();
+    }
+    _subscribe(subscriber) {
+        const subscription = super._subscribe(subscriber);
+        !subscription.closed && subscriber.next(this._value);
+        return subscription;
+    }
+    getValue() {
+        const { hasError, thrownError, _value } = this;
+        if (hasError) {
+            throw thrownError;
+        }
+        this._throwIfClosed();
+        return _value;
+    }
+    next(value) {
+        super.next((this._value = value));
+    }
+}
+//# sourceMappingURL=BehaviorSubject.js.map