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/postcss-normalize-charset/src/index.js

@@ -0,0 +1,56 @@
+'use strict';
+const charset = 'charset';
+// eslint-disable-next-line no-control-regex
+const nonAscii = /[^\x00-\x7F]/;
+
+/**
+ * @typedef {{add?: boolean}} Options
+ */
+/**
+ * @type {import('postcss').PluginCreator<Options>}
+ * @param {Options} opts
+ * @return {import('postcss').Plugin}
+ */
+function pluginCreator(opts = {}) {
+  return {
+    postcssPlugin: 'postcss-normalize-' + charset,
+
+    OnceExit(css, { AtRule }) {
+      /** @type {import('postcss').AtRule | undefined} */
+      let charsetRule;
+      /** @type {import('postcss').Node | undefined} */
+      let nonAsciiNode;
+
+      css.walk((node) => {
+        if (node.type === 'atrule' && node.name === charset) {
+          if (!charsetRule) {
+            charsetRule = node;
+          }
+          node.remove();
+        } else if (
+          !nonAsciiNode &&
+          node.parent === css &&
+          nonAscii.test(node.toString())
+        ) {
+          nonAsciiNode = node;
+        }
+      });
+
+      if (nonAsciiNode) {
+        if (!charsetRule && opts.add !== false) {
+          charsetRule = new AtRule({
+            name: charset,
+            params: '"utf-8"',
+          });
+        }
+        if (charsetRule) {
+          charsetRule.source = nonAsciiNode.source;
+          css.prepend(charsetRule);
+        }
+      }
+    },
+  };
+}
+
+pluginCreator.postcss = true;
+module.exports = pluginCreator;