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/strip-final-newline/index.js

@@ -0,0 +1,16 @@
+'use strict';
+
+module.exports = input => {
+	const LF = typeof input === 'string' ? '\n' : '\n'.charCodeAt();
+	const CR = typeof input === 'string' ? '\r' : '\r'.charCodeAt();
+
+	if (input[input.length - 1] === LF) {
+		input = input.slice(0, input.length - 1);
+	}
+
+	if (input[input.length - 1] === CR) {
+		input = input.slice(0, input.length - 1);
+	}
+
+	return input;
+};