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/asynckit/bench.js

@@ -0,0 +1,76 @@
+/* eslint no-console: "off" */
+
+var asynckit = require('./')
+  , async    = require('async')
+  , assert   = require('assert')
+  , expected = 0
+  ;
+
+var Benchmark = require('benchmark');
+var suite = new Benchmark.Suite;
+
+var source = [];
+for (var z = 1; z < 100; z++)
+{
+  source.push(z);
+  expected += z;
+}
+
+suite
+// add tests
+
+.add('async.map', function(deferred)
+{
+  var total = 0;
+
+  async.map(source,
+  function(i, cb)
+  {
+    setImmediate(function()
+    {
+      total += i;
+      cb(null, total);
+    });
+  },
+  function(err, result)
+  {
+    assert.ifError(err);
+    assert.equal(result[result.length - 1], expected);
+    deferred.resolve();
+  });
+}, {'defer': true})
+
+
+.add('asynckit.parallel', function(deferred)
+{
+  var total = 0;
+
+  asynckit.parallel(source,
+  function(i, cb)
+  {
+    setImmediate(function()
+    {
+      total += i;
+      cb(null, total);
+    });
+  },
+  function(err, result)
+  {
+    assert.ifError(err);
+    assert.equal(result[result.length - 1], expected);
+    deferred.resolve();
+  });
+}, {'defer': true})
+
+
+// add listeners
+.on('cycle', function(ev)
+{
+  console.log(String(ev.target));
+})
+.on('complete', function()
+{
+  console.log('Fastest is ' + this.filter('fastest').map('name'));
+})
+// run async
+.run({ 'async': true });