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/eslint-plugin-import/docs/rules/no-useless-path-segments.md

@@ -0,0 +1,85 @@
+# import/no-useless-path-segments
+
+🔧 This rule is automatically fixable by the [`--fix` CLI option](https://eslint.org/docs/latest/user-guide/command-line-interface#--fix).
+
+<!-- end auto-generated rule header -->
+
+Use this rule to prevent unnecessary path segments in import and require statements.
+
+## Rule Details
+
+Given the following folder structure:
+
+```pt
+my-project
+├── app.js
+├── footer.js
+├── header.js
+└── helpers.js
+└── helpers
+    └── index.js
+├── index.js
+└── pages
+    ├── about.js
+    ├── contact.js
+    └── index.js
+```
+
+The following patterns are considered problems:
+
+```js
+/**
+ *  in my-project/app.js
+ */
+
+import "./../my-project/pages/about.js"; // should be "./pages/about.js"
+import "./../my-project/pages/about"; // should be "./pages/about"
+import "../my-project/pages/about.js"; // should be "./pages/about.js"
+import "../my-project/pages/about"; // should be "./pages/about"
+import "./pages//about"; // should be "./pages/about"
+import "./pages/"; // should be "./pages"
+import "./pages/index"; // should be "./pages" (except if there is a ./pages.js file)
+import "./pages/index.js"; // should be "./pages" (except if there is a ./pages.js file)
+```
+
+The following patterns are NOT considered problems:
+
+```js
+/**
+ *  in my-project/app.js
+ */
+
+import "./header.js";
+import "./pages";
+import "./pages/about";
+import ".";
+import "..";
+import fs from "fs";
+```
+
+## Options
+
+### noUselessIndex
+
+If you want to detect unnecessary `/index` or `/index.js` (depending on the specified file extensions, see below) imports in your paths, you can enable the option `noUselessIndex`. By default it is set to `false`:
+
+```js
+"import/no-useless-path-segments": ["error", {
+  noUselessIndex: true,
+}]
+```
+
+Additionally to the patterns described above, the following imports are considered problems if `noUselessIndex` is enabled:
+
+```js
+// in my-project/app.js
+import "./helpers/index"; // should be "./helpers/" (not auto-fixable to `./helpers` because this would lead to an ambiguous import of `./helpers.js` and `./helpers/index.js`)
+import "./pages/index"; // should be "./pages" (auto-fixable)
+import "./pages/index.js"; // should be "./pages" (auto-fixable)
+```
+
+Note: `noUselessIndex` only avoids ambiguous imports for `.js` files if you haven't specified other resolved file extensions. See [Settings: import/extensions](https://github.com/import-js/eslint-plugin-import#importextensions) for details.
+
+### commonjs
+
+When set to `true`, this rule checks CommonJS imports. Default to `false`.