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/core-js-compat/external.json

@@ -0,0 +1,21 @@
+{
+  "modules": {
+    "android": "61",
+    "bun": "0.1.1",
+    "chrome": "61",
+    "chrome-android": "61",
+    "deno": "1.0",
+    "edge": "16",
+    "firefox": "60",
+    "firefox-android": "60",
+    "ios": "10.3",
+    "node": "13.2",
+    "oculus": "4.0",
+    "opera": "48",
+    "opera-android": "45",
+    "opera_mobile": "45",
+    "quest": "4.0",
+    "safari": "10.1",
+    "samsung": "8.0"
+  }
+}