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/webpack/lib/rules/BasicEffectRulePlugin.js

@@ -0,0 +1,59 @@
+/*
+	MIT License http://www.opensource.org/licenses/mit-license.php
+	Author Tobias Koppers @sokra
+*/
+
+"use strict";
+
+/** @typedef {import("../../declarations/WebpackOptions").RuleSetRule} RuleSetRule */
+/** @typedef {import("./RuleSetCompiler")} RuleSetCompiler */
+
+/**
+ * Defines the keys of types type used by this module.
+ * @template T
+ * @template {T[keyof T]} V
+ * @typedef {import("./RuleSetCompiler").KeysOfTypes<T, V>} KeysOfTypes
+ */
+
+/** @typedef {KeysOfTypes<RuleSetRule, string | boolean | { [k: string]: EXPECTED_ANY }>} BasicEffectRuleKeys */
+
+const PLUGIN_NAME = "BasicEffectRulePlugin";
+
+class BasicEffectRulePlugin {
+	/**
+	 * Creates an instance of BasicEffectRulePlugin.
+	 * @param {BasicEffectRuleKeys} ruleProperty the rule property
+	 * @param {string=} effectType the effect type
+	 */
+	constructor(ruleProperty, effectType) {
+		/** @type {BasicEffectRuleKeys} */
+		this.ruleProperty = ruleProperty;
+		/** @type {string | BasicEffectRuleKeys} */
+		this.effectType = effectType || ruleProperty;
+	}
+
+	/**
+	 * Applies the plugin by registering its hooks on the compiler.
+	 * @param {RuleSetCompiler} ruleSetCompiler the rule set compiler
+	 * @returns {void}
+	 */
+	apply(ruleSetCompiler) {
+		ruleSetCompiler.hooks.rule.tap(
+			PLUGIN_NAME,
+			(path, rule, unhandledProperties, result) => {
+				if (unhandledProperties.has(this.ruleProperty)) {
+					unhandledProperties.delete(this.ruleProperty);
+
+					const value = rule[this.ruleProperty];
+
+					result.effects.push({
+						type: this.effectType,
+						value
+					});
+				}
+			}
+		);
+	}
+}
+
+module.exports = BasicEffectRulePlugin;