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/json5/lib/register.js

@@ -0,0 +1,13 @@
+const fs = require('fs')
+const JSON5 = require('./')
+
+// eslint-disable-next-line node/no-deprecated-api
+require.extensions['.json5'] = function (module, filename) {
+    const content = fs.readFileSync(filename, 'utf8')
+    try {
+        module.exports = JSON5.parse(content)
+    } catch (err) {
+        err.message = filename + ': ' + err.message
+        throw err
+    }
+}