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/justify-content.js

@@ -0,0 +1,54 @@
+let Declaration = require('../declaration')
+let flexSpec = require('./flex-spec')
+
+class JustifyContent extends Declaration {
+  /**
+   * Return property name by final spec
+   */
+  normalize() {
+    return 'justify-content'
+  }
+
+  /**
+   * Change property name for 2009 and 2012 specs
+   */
+  prefixed(prop, prefix) {
+    let spec
+    ;[spec, prefix] = flexSpec(prefix)
+    if (spec === 2009) {
+      return prefix + 'box-pack'
+    }
+    if (spec === 2012) {
+      return prefix + 'flex-pack'
+    }
+    return super.prefixed(prop, prefix)
+  }
+
+  /**
+   * Change value for 2009 and 2012 specs
+   */
+  set(decl, prefix) {
+    let spec = flexSpec(prefix)[0]
+    if (spec === 2009 || spec === 2012) {
+      let value = JustifyContent.oldValues[decl.value] || decl.value
+      decl.value = value
+      if (spec !== 2009 || value !== 'distribute') {
+        return super.set(decl, prefix)
+      }
+    } else if (spec === 'final') {
+      return super.set(decl, prefix)
+    }
+    return undefined
+  }
+}
+
+JustifyContent.names = ['justify-content', 'flex-pack', 'box-pack']
+
+JustifyContent.oldValues = {
+  'flex-end': 'end',
+  'flex-start': 'start',
+  'space-around': 'distribute',
+  'space-between': 'justify'
+}
+
+module.exports = JustifyContent