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/flex-basis.js

@@ -0,0 +1,39 @@
+let Declaration = require('../declaration')
+let flexSpec = require('./flex-spec')
+
+class FlexBasis extends Declaration {
+  /**
+   * Return property name by final spec
+   */
+  normalize() {
+    return 'flex-basis'
+  }
+
+  /**
+   * Return flex property for 2012 spec
+   */
+  prefixed(prop, prefix) {
+    let spec
+    ;[spec, prefix] = flexSpec(prefix)
+    if (spec === 2012) {
+      return prefix + 'flex-preferred-size'
+    }
+    return super.prefixed(prop, prefix)
+  }
+
+  /**
+   * Ignore 2009 spec and use flex property for 2012
+   */
+  set(decl, prefix) {
+    let spec
+    ;[spec, prefix] = flexSpec(prefix)
+    if (spec === 2012 || spec === 'final') {
+      return super.set(decl, prefix)
+    }
+    return undefined
+  }
+}
+
+FlexBasis.names = ['flex-basis', 'flex-preferred-size']
+
+module.exports = FlexBasis