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/onetime/index.d.ts

@@ -0,0 +1,64 @@
+declare namespace onetime {
+	interface Options {
+		/**
+		Throw an error when called more than once.
+
+		@default false
+		*/
+		throw?: boolean;
+	}
+}
+
+declare const onetime: {
+	/**
+	Ensure a function is only called once. When called multiple times it will return the return value from the first call.
+
+	@param fn - Function that should only be called once.
+	@returns A function that only calls `fn` once.
+
+	@example
+	```
+	import onetime = require('onetime');
+
+	let i = 0;
+
+	const foo = onetime(() => ++i);
+
+	foo(); //=> 1
+	foo(); //=> 1
+	foo(); //=> 1
+
+	onetime.callCount(foo); //=> 3
+	```
+	*/
+	<ArgumentsType extends unknown[], ReturnType>(
+		fn: (...arguments: ArgumentsType) => ReturnType,
+		options?: onetime.Options
+	): (...arguments: ArgumentsType) => ReturnType;
+
+	/**
+	Get the number of times `fn` has been called.
+
+	@param fn - Function to get call count from.
+	@returns A number representing how many times `fn` has been called.
+
+	@example
+	```
+	import onetime = require('onetime');
+
+	const foo = onetime(() => {});
+	foo();
+	foo();
+	foo();
+
+	console.log(onetime.callCount(foo));
+	//=> 3
+	```
+	*/
+	callCount(fn: (...arguments: any[]) => unknown): number;
+
+	// TODO: Remove this for the next major release
+	default: typeof onetime;
+};
+
+export = onetime;