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/spdx-correct/README.md

@@ -0,0 +1,22 @@
+## Usage
+
+```javascript
+var correct = require('spdx-correct')
+var assert = require('assert')
+
+assert.strictEqual(correct('mit'), 'MIT')
+
+assert.strictEqual(correct('Apache 2'), 'Apache-2.0')
+
+assert(correct('No idea what license') === null)
+
+// disable upgrade option
+assert(correct('GPL-3.0'), 'GPL-3.0-or-later')
+assert(correct('GPL-3.0', { upgrade: false }), 'GPL-3.0')
+```
+
+## Contributors
+
+spdx-correct has benefited from the work of several contributors.
+See [the GitHub repository](https://github.com/jslicense/spdx-correct.js/graphs/contributors)
+for more information.