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/node-int64/package.json

@@ -0,0 +1,27 @@
+{
+  "name": "node-int64",
+  "description": "Support for representing 64-bit integers in JavaScript",
+  "url": "http://github.com/broofa/node-int64",
+  "keywords": [
+    "math",
+    "integer",
+    "int64"
+  ],
+  "author": "Robert Kieffer <robert@broofa.com>",
+  "contributors": [],
+  "dependencies": {},
+  "license": "MIT",
+  "lib": ".",
+  "main": "./Int64.js",
+  "version": "0.4.0",
+  "scripts": {
+    "test": "nodeunit test.js"
+  },
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/broofa/node-int64"
+  },
+  "devDependencies": {
+    "nodeunit": "^0.9.0"
+  }
+}