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/loader-utils/package.json

@@ -0,0 +1,39 @@
+{
+  "name": "loader-utils",
+  "version": "2.0.4",
+  "author": "Tobias Koppers @sokra",
+  "description": "utils for webpack loaders",
+  "dependencies": {
+    "big.js": "^5.2.2",
+    "emojis-list": "^3.0.0",
+    "json5": "^2.1.2"
+  },
+  "scripts": {
+    "lint": "eslint lib test",
+    "pretest": "yarn lint",
+    "test": "jest",
+    "test:ci": "jest --coverage",
+    "release": "yarn test && standard-version"
+  },
+  "license": "MIT",
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/webpack/loader-utils.git"
+  },
+  "engines": {
+    "node": ">=8.9.0"
+  },
+  "devDependencies": {
+    "coveralls": "^3.0.9",
+    "eslint": "^6.8.0",
+    "eslint-plugin-node": "^11.0.0",
+    "eslint-plugin-prettier": "^3.1.2",
+    "jest": "^25.1.0",
+    "prettier": "^1.19.1",
+    "standard-version": "^7.1.0"
+  },
+  "main": "lib/index.js",
+  "files": [
+    "lib"
+  ]
+}