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/@wordpress/components/build-module/toolbar/toolbar-context/index.js

@@ -0,0 +1,12 @@
+/**
+ * External dependencies
+ */
+// eslint-disable-next-line no-restricted-imports
+
+/**
+ * WordPress dependencies
+ */
+import { createContext } from '@wordpress/element';
+const ToolbarContext = createContext(undefined);
+export default ToolbarContext;
+//# sourceMappingURL=index.js.map

node_modules/@wordpress/components/build-module/toolbar/toolbar-context/index.js.map

@@ -0,0 +1 @@
+{"version":3,"names":["createContext","ToolbarContext","undefined"],"sources":["@wordpress/components/src/toolbar/toolbar-context/index.ts"],"sourcesContent":["/**\n * External dependencies\n */\n// eslint-disable-next-line no-restricted-imports\nimport type * as Ariakit from '@ariakit/react';\n\n/**\n * WordPress dependencies\n */\nimport { createContext } from '@wordpress/element';\n\nconst ToolbarContext = createContext< Ariakit.ToolbarStore | undefined >(\n\tundefined\n);\n\nexport default ToolbarContext;\n"],"mappings":"AAAA;AACA;AACA;AACA;;AAGA;AACA;AACA;AACA,SAASA,aAAa,QAAQ,oBAAoB;AAElD,MAAMC,cAAc,GAAGD,aAAa,CACnCE,SACD,CAAC;AAED,eAAeD,cAAc"}