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/encoding/package.json

@@ -0,0 +1,18 @@
+{
+    "name": "encoding",
+    "version": "0.1.13",
+    "description": "Convert encodings, uses iconv-lite",
+    "main": "lib/encoding.js",
+    "scripts": {
+        "test": "nodeunit test"
+    },
+    "repository": "https://github.com/andris9/encoding.git",
+    "author": "Andris Reinman",
+    "license": "MIT",
+    "dependencies": {
+        "iconv-lite": "^0.6.2"
+    },
+    "devDependencies": {
+        "nodeunit": "0.11.3"
+    }
+}