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/deepmerge/rollup.config.js

@@ -0,0 +1,22 @@
+import resolve from 'rollup-plugin-node-resolve'
+import commonjs from 'rollup-plugin-commonjs'
+import pkg from './package.json'
+
+export default {
+	input: `index.js`,
+	plugins: [
+		commonjs(),
+		resolve(),
+	],
+	output: [
+		{
+			file: pkg.main,
+			format: `cjs`
+		},
+		{
+			name: 'deepmerge',
+			file: 'dist/umd.js',
+			format: `umd`
+		},
+	],
+}