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/exit/Gruntfile.js

@@ -0,0 +1,48 @@
+'use strict';
+
+module.exports = function(grunt) {
+
+  // Project configuration.
+  grunt.initConfig({
+    nodeunit: {
+      files: ['test/**/*_test.js'],
+    },
+    jshint: {
+      options: {
+        jshintrc: '.jshintrc'
+      },
+      gruntfile: {
+        src: 'Gruntfile.js'
+      },
+      lib: {
+        src: ['lib/**/*.js']
+      },
+      test: {
+        src: ['test/**/*.js']
+      },
+    },
+    watch: {
+      gruntfile: {
+        files: '<%= jshint.gruntfile.src %>',
+        tasks: ['jshint:gruntfile']
+      },
+      lib: {
+        files: '<%= jshint.lib.src %>',
+        tasks: ['jshint:lib', 'nodeunit']
+      },
+      test: {
+        files: '<%= jshint.test.src %>',
+        tasks: ['jshint:test', 'nodeunit']
+      },
+    },
+  });
+
+  // These plugins provide necessary tasks.
+  grunt.loadNpmTasks('grunt-contrib-nodeunit');
+  grunt.loadNpmTasks('grunt-contrib-jshint');
+  grunt.loadNpmTasks('grunt-contrib-watch');
+
+  // Default task.
+  grunt.registerTask('default', ['jshint', 'nodeunit']);
+
+};