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/isarray/LICENSE

@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2013 Julian Gruber <julian@juliangruber.com>
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

node_modules/isarray/README.md

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+
+# isarray
+
+`Array#isArray` for older browsers and deprecated Node.js versions.
+
+[![build status](https://secure.travis-ci.org/juliangruber/isarray.svg)](http://travis-ci.org/juliangruber/isarray)
+[![downloads](https://img.shields.io/npm/dm/isarray.svg)](https://www.npmjs.org/package/isarray)
+
+[![browser support](https://ci.testling.com/juliangruber/isarray.png)
+](https://ci.testling.com/juliangruber/isarray)
+
+__Just use Array.isArray directly__, unless you need to support those older versions.
+
+## Usage
+
+```js
+var isArray = require('isarray');
+
+console.log(isArray([])); // => true
+console.log(isArray({})); // => false
+```
+
+## Installation
+
+With [npm](https://npmjs.org) do
+
+```bash
+$ npm install isarray
+```
+
+Then bundle for the browser with
+[browserify](https://github.com/substack/node-browserify).
+
+## Sponsors
+
+This module is proudly supported by my [Sponsors](https://github.com/juliangruber/sponsors)!
+
+Do you want to support modules like this to improve their quality, stability and weigh in on new features? Then please consider donating to my [Patreon](https://www.patreon.com/juliangruber). Not sure how much of my modules you're using? Try [feross/thanks](https://github.com/feross/thanks)!

node_modules/isarray/index.js

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+var toString = {}.toString;
+
+module.exports = Array.isArray || function (arr) {
+  return toString.call(arr) == '[object Array]';
+};

node_modules/isarray/package.json

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+{
+  "name": "isarray",
+  "description": "Array#isArray for older browsers",
+  "version": "2.0.5",
+  "repository": {
+    "type": "git",
+    "url": "git://github.com/juliangruber/isarray.git"
+  },
+  "homepage": "https://github.com/juliangruber/isarray",
+  "main": "index.js",
+  "files": [
+    "index.js"
+  ],
+  "dependencies": {},
+  "devDependencies": {
+    "tape": "~2.13.4"
+  },
+  "keywords": [
+    "browser",
+    "isarray",
+    "array"
+  ],
+  "author": {
+    "name": "Julian Gruber",
+    "email": "mail@juliangruber.com",
+    "url": "http://juliangruber.com"
+  },
+  "license": "MIT",
+  "testling": {
+    "files": "test.js",
+    "browsers": [
+      "ie/8..latest",
+      "firefox/17..latest",
+      "firefox/nightly",
+      "chrome/22..latest",
+      "chrome/canary",
+      "opera/12..latest",
+      "opera/next",
+      "safari/5.1..latest",
+      "ipad/6.0..latest",
+      "iphone/6.0..latest",
+      "android-browser/4.2..latest"
+    ]
+  },
+  "scripts": {
+    "test": "tape test.js"
+  }
+}