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/validate-npm-package-license/package.json

@@ -0,0 +1,28 @@
+{
+  "name": "validate-npm-package-license",
+  "description": "Give me a string and I'll tell you if it's a valid npm package license string",
+  "version": "3.0.4",
+  "author": "Kyle E. Mitchell <kyle@kemitchell.com> (https://kemitchell.com)",
+  "contributors": [
+    "Mark Stacey <markjstacey@gmail.com>"
+  ],
+  "dependencies": {
+    "spdx-correct": "^3.0.0",
+    "spdx-expression-parse": "^3.0.0"
+  },
+  "devDependencies": {
+    "defence-cli": "^2.0.1",
+    "replace-require-self": "^1.0.0"
+  },
+  "keywords": [
+    "license",
+    "npm",
+    "package",
+    "validation"
+  ],
+  "license": "Apache-2.0",
+  "repository": "kemitchell/validate-npm-package-license.js",
+  "scripts": {
+    "test": "defence README.md | replace-require-self | node"
+  }
+}