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-unique-selectors/src/index.js

@@ -0,0 +1,59 @@
+'use strict';
+const selectorParser = require('postcss-selector-parser');
+
+/**
+ * @param {string} selectors
+ * @param {selectorParser.SyncProcessor<void>} callback
+ * @return {string}
+ */
+function parseSelectors(selectors, callback) {
+  return selectorParser(callback).processSync(selectors);
+}
+
+/**
+ * @param {import('postcss').Rule} rule
+ * @return {string}
+ */
+function unique(rule) {
+  const selector = [...new Set(rule.selectors)];
+  selector.sort();
+  return selector.join();
+}
+
+/**
+ * @type {import('postcss').PluginCreator<void>}
+ * @return {import('postcss').Plugin}
+ */
+function pluginCreator() {
+  return {
+    postcssPlugin: 'postcss-unique-selectors',
+    OnceExit(css) {
+      css.walkRules((nodes) => {
+        /** @type {string[]} */
+        let comments = [];
+        /** @type {selectorParser.SyncProcessor<void>} */
+        const removeAndSaveComments = (selNode) => {
+          selNode.walk((sel) => {
+            if (sel.type === 'comment') {
+              comments.push(sel.value);
+              sel.remove();
+              return;
+            } else {
+              return;
+            }
+          });
+        };
+        if (nodes.raws.selector && nodes.raws.selector.raw) {
+          parseSelectors(nodes.raws.selector.raw, removeAndSaveComments);
+          nodes.raws.selector.raw = unique(nodes);
+        }
+        nodes.selector = parseSelectors(nodes.selector, removeAndSaveComments);
+        nodes.selector = unique(nodes);
+        nodes.selectors = nodes.selectors.concat(comments);
+      });
+    },
+  };
+}
+
+pluginCreator.postcss = true;
+module.exports = pluginCreator;