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/loose-envify/loose-envify.js

@@ -0,0 +1,36 @@
+'use strict';
+
+var stream = require('stream');
+var util = require('util');
+var replace = require('./replace');
+
+var jsonExtRe = /\.json$/;
+
+module.exports = function(rootEnv) {
+  rootEnv = rootEnv || process.env;
+  return function (file, trOpts) {
+    if (jsonExtRe.test(file)) {
+      return stream.PassThrough();
+    }
+    var envs = trOpts ? [rootEnv, trOpts] : [rootEnv];
+    return new LooseEnvify(envs);
+  };
+};
+
+function LooseEnvify(envs) {
+  stream.Transform.call(this);
+  this._data = '';
+  this._envs = envs;
+}
+util.inherits(LooseEnvify, stream.Transform);
+
+LooseEnvify.prototype._transform = function(buf, enc, cb) {
+  this._data += buf;
+  cb();
+};
+
+LooseEnvify.prototype._flush = function(cb) {
+  var replaced = replace(this._data, this._envs);
+  this.push(replaced);
+  cb();
+};