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/tapable/lib/MultiHook.js

@@ -0,0 +1,52 @@
+/*
+	MIT License http://www.opensource.org/licenses/mit-license.php
+	Author Tobias Koppers @sokra
+*/
+"use strict";
+
+class MultiHook {
+	constructor(hooks, name = undefined) {
+		this.hooks = hooks;
+		this.name = name;
+	}
+
+	tap(options, fn) {
+		for (const hook of this.hooks) {
+			hook.tap(options, fn);
+		}
+	}
+
+	tapAsync(options, fn) {
+		for (const hook of this.hooks) {
+			hook.tapAsync(options, fn);
+		}
+	}
+
+	tapPromise(options, fn) {
+		for (const hook of this.hooks) {
+			hook.tapPromise(options, fn);
+		}
+	}
+
+	isUsed() {
+		for (const hook of this.hooks) {
+			if (hook.isUsed()) return true;
+		}
+		return false;
+	}
+
+	intercept(interceptor) {
+		for (const hook of this.hooks) {
+			hook.intercept(interceptor);
+		}
+	}
+
+	withOptions(options) {
+		return new MultiHook(
+			this.hooks.map((hook) => hook.withOptions(options)),
+			this.name
+		);
+	}
+}
+
+module.exports = MultiHook;