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/crypto-random-string/index.d.ts

@@ -0,0 +1,17 @@
+/**
+Generate a [cryptographically strong](https://en.m.wikipedia.org/wiki/Strong_cryptography) random string.
+
+@param length - Length of the returned string.
+@returns A [`hex`](https://en.wikipedia.org/wiki/Hexadecimal) string.
+
+@example
+```
+import cryptoRandomString = require('crypto-random-string');
+
+cryptoRandomString(10);
+//=> '2cf05d94db'
+```
+*/
+declare function cryptoRandomString(length: number): string;
+
+export = cryptoRandomString;