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/@emotion/use-insertion-effect-with-fallbacks/src/conditions/false.ts

@@ -0,0 +1 @@
+export default false

node_modules/@emotion/use-insertion-effect-with-fallbacks/src/conditions/is-browser.ts

@@ -0,0 +1 @@
+export default typeof document !== 'undefined'

node_modules/@emotion/use-insertion-effect-with-fallbacks/src/conditions/true.ts

@@ -0,0 +1 @@
+export default true

node_modules/@emotion/use-insertion-effect-with-fallbacks/src/index.ts

@@ -0,0 +1,21 @@
+import * as React from 'react'
+import isBrowser from '#is-browser'
+
+const syncFallback = <T>(create: () => T) => create()
+
+const useInsertionEffect = React[
+  ('useInsertion' + 'Effect') as 'useInsertionEffect'
+]
+  ? (React[('useInsertion' + 'Effect') as 'useInsertionEffect'] as <T>(
+      create: () => T
+    ) => T | undefined)
+  : false
+
+export const useInsertionEffectAlwaysWithSyncFallback: <T>(
+  create: () => T
+) => T | undefined = !isBrowser
+  ? syncFallback
+  : useInsertionEffect || syncFallback
+
+export const useInsertionEffectWithLayoutFallback: typeof React.useLayoutEffect =
+  useInsertionEffect || React.useLayoutEffect