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/web-vitals/dist/modules/lib/observe.d.ts

@@ -0,0 +1,20 @@
+import { FirstInputPolyfillEntry, NavigationTimingPolyfillEntry } from '../types.js';
+interface PerformanceEntryMap {
+    'event': PerformanceEventTiming[];
+    'paint': PerformancePaintTiming[];
+    'layout-shift': LayoutShift[];
+    'largest-contentful-paint': LargestContentfulPaint[];
+    'first-input': PerformanceEventTiming[] | FirstInputPolyfillEntry[];
+    'navigation': PerformanceNavigationTiming[] | NavigationTimingPolyfillEntry[];
+    'resource': PerformanceResourceTiming[];
+}
+/**
+ * Takes a performance entry type and a callback function, and creates a
+ * `PerformanceObserver` instance that will observe the specified entry type
+ * with buffering enabled and call the callback _for each entry_.
+ *
+ * This function also feature-detects entry support and wraps the logic in a
+ * try/catch to avoid errors in unsupporting browsers.
+ */
+export declare const observe: <K extends keyof PerformanceEntryMap>(type: K, callback: (entries: PerformanceEntryMap[K]) => void, opts?: PerformanceObserverInit) => PerformanceObserver | undefined;
+export {};