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/cssom/README.mdown

@@ -0,0 +1,67 @@
+# CSSOM
+
+CSSOM.js is a CSS parser written in pure JavaScript. It is also a partial implementation of [CSS Object Model](http://dev.w3.org/csswg/cssom/). 
+
+    CSSOM.parse("body {color: black}")
+    -> {
+      cssRules: [
+        {
+          selectorText: "body",
+          style: {
+            0: "color",
+            color: "black",
+            length: 1
+          }
+        }
+      ]
+    }
+
+
+## [Parser demo](http://nv.github.com/CSSOM/docs/parse.html)
+
+Works well in Google Chrome 6+, Safari 5+, Firefox 3.6+, Opera 10.63+.
+Doesn't work in IE < 9 because of unsupported getters/setters.
+
+To use CSSOM.js in the browser you might want to build a one-file version that exposes a single `CSSOM` global variable:
+
+    ➤ git clone https://github.com/NV/CSSOM.git
+    ➤ cd CSSOM
+    ➤ node build.js
+    build/CSSOM.js is done
+
+To use it with Node.js or any other CommonJS loader:
+
+    ➤ npm install cssom
+
+## Don’t use it if...
+
+You parse CSS to mungle, minify or reformat code like this:
+
+```css
+div {
+  background: gray;
+  background: linear-gradient(to bottom, white 0%, black 100%);
+}
+```
+
+This pattern is often used to give browsers that don’t understand linear gradients a fallback solution (e.g. gray color in the example).
+In CSSOM, `background: gray` [gets overwritten](http://nv.github.io/CSSOM/docs/parse.html#css=div%20%7B%0A%20%20%20%20%20%20background%3A%20gray%3B%0A%20%20%20%20background%3A%20linear-gradient(to%20bottom%2C%20white%200%25%2C%20black%20100%25)%3B%0A%7D).
+It does **NOT** get preserved.
+
+If you do CSS mungling, minification, or image inlining, considere using one of the following:
+
+  * [postcss](https://github.com/postcss/postcss)
+  * [reworkcss/css](https://github.com/reworkcss/css)
+  * [csso](https://github.com/css/csso)
+  * [mensch](https://github.com/brettstimmerman/mensch)
+
+
+## [Tests](http://nv.github.com/CSSOM/spec/)
+
+To run tests locally:
+
+    ➤ git submodule init
+    ➤ git submodule update
+
+
+## [Who uses CSSOM.js](https://github.com/NV/CSSOM/wiki/Who-uses-CSSOM.js)