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/markdownlint/lib/md035.js

@@ -0,0 +1,21 @@
+// @ts-check
+
+"use strict";
+
+const { addErrorDetailIf, filterTokens } = require("../helpers");
+
+module.exports = {
+  "names": [ "MD035", "hr-style" ],
+  "description": "Horizontal rule style",
+  "tags": [ "hr" ],
+  "function": function MD035(params, onError) {
+    let style = String(params.config.style || "consistent");
+    filterTokens(params, "hr", (token) => {
+      const { lineNumber, markup } = token;
+      if (style === "consistent") {
+        style = markup;
+      }
+      addErrorDetailIf(onError, lineNumber, style, markup);
+    });
+  }
+};