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/teex/example.js

@@ -0,0 +1,16 @@
+const tee = require('./')
+const { Readable } = require('streamx')
+
+const s = new Readable()
+
+for (let i = 0; i < 1000; i++) {
+  s.push(Buffer.alloc(1024))
+}
+
+const [a, b] = tee(s)
+
+a.on('data', console.log)
+
+setTimeout(function () {
+  b.read()
+}, 1000)