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/autoprefixer/lib/hacks/border-image.js

@@ -0,0 +1,15 @@
+let Declaration = require('../declaration')
+
+class BorderImage extends Declaration {
+  /**
+   * Remove fill parameter for prefixed declarations
+   */
+  set(decl, prefix) {
+    decl.value = decl.value.replace(/\s+fill(\s)/, '$1')
+    return super.set(decl, prefix)
+  }
+}
+
+BorderImage.names = ['border-image']
+
+module.exports = BorderImage