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/md047.js

@@ -0,0 +1,28 @@
+// @ts-check
+
+"use strict";
+
+const { addError, isBlankLine } = require("../helpers");
+
+module.exports = {
+  "names": [ "MD047", "single-trailing-newline" ],
+  "description": "Files should end with a single newline character",
+  "tags": [ "blank_lines" ],
+  "function": function MD047(params, onError) {
+    const lastLineNumber = params.lines.length;
+    const lastLine = params.lines[lastLineNumber - 1];
+    if (!isBlankLine(lastLine)) {
+      addError(
+        onError,
+        lastLineNumber,
+        null,
+        null,
+        [ lastLine.length, 1 ],
+        {
+          "insertText": "\n",
+          "editColumn": lastLine.length + 1
+        }
+      );
+    }
+  }
+};