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/stylelint-scss/dist/utils/removeEmptyLinesBefore.js

@@ -0,0 +1,11 @@
+"use strict";
+
+Object.defineProperty(exports, "__esModule", {
+  value: true
+});
+exports.removeEmptyLinesBefore = removeEmptyLinesBefore;
+// Remove empty lines before a node. Mutates the node.
+function removeEmptyLinesBefore(node /*: postcss$node*/, newline /*: '\n' | '\r\n'*/) /*: postcss$node*/{
+  node.raws.before = node.raws.before.replace(/(\r?\n\s*\n)+/g, newline);
+  return node;
+}