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/postcss/lib/root.js

@@ -0,0 +1,61 @@
+'use strict'
+
+let Container = require('./container')
+
+let LazyResult, Processor
+
+class Root extends Container {
+  constructor(defaults) {
+    super(defaults)
+    this.type = 'root'
+    if (!this.nodes) this.nodes = []
+  }
+
+  normalize(child, sample, type) {
+    let nodes = super.normalize(child)
+
+    if (sample) {
+      if (type === 'prepend') {
+        if (this.nodes.length > 1) {
+          sample.raws.before = this.nodes[1].raws.before
+        } else {
+          delete sample.raws.before
+        }
+      } else if (this.first !== sample) {
+        for (let node of nodes) {
+          node.raws.before = sample.raws.before
+        }
+      }
+    }
+
+    return nodes
+  }
+
+  removeChild(child, ignore) {
+    let index = this.index(child)
+
+    if (!ignore && index === 0 && this.nodes.length > 1) {
+      this.nodes[1].raws.before = this.nodes[index].raws.before
+    }
+
+    return super.removeChild(child)
+  }
+
+  toResult(opts = {}) {
+    let lazy = new LazyResult(new Processor(), this, opts)
+    return lazy.stringify()
+  }
+}
+
+Root.registerLazyResult = dependant => {
+  LazyResult = dependant
+}
+
+Root.registerProcessor = dependant => {
+  Processor = dependant
+}
+
+module.exports = Root
+Root.default = Root
+
+Container.registerRoot(Root)