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/cli.js

@@ -0,0 +1,16 @@
+#!/usr/bin/env node
+'use strict';
+
+var looseEnvify = require('./');
+var fs = require('fs');
+
+if (process.argv[2]) {
+  fs.createReadStream(process.argv[2], {encoding: 'utf8'})
+    .pipe(looseEnvify(process.argv[2]))
+    .pipe(process.stdout);
+} else {
+  process.stdin.resume()
+  process.stdin
+    .pipe(looseEnvify(__filename))
+    .pipe(process.stdout);
+}