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/hpack.js/bin/benchmark

@@ -0,0 +1,34 @@
+#!/usr/bin/env node
+var hpack = require('../');
+
+var options = {
+  table: { size: 1024 }
+};
+
+var compressor = hpack.compressor.create(options);
+
+var vector = [];
+for (var i = 0; i < 1024; i++) {
+  vector.push({
+    name: 'kind-of-big-header-name__',
+    value: 'not-so-small value yes!',
+    huffman: true,
+    neverIndex: true
+  });
+}
+compressor.write(vector);
+var input = compressor.read();
+
+console.time('decompressor');
+for (var i = 0; i < 2000; i++) {
+  var decompressor = hpack.decompressor.create(options);
+
+  decompressor.write(input);
+  decompressor.execute();
+  while (true) {
+    var chunk = decompressor.read();
+    if (!chunk)
+      break;
+  }
+}
+console.timeEnd('decompressor');