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/npm-normalize-package-bin/test/string.js

@@ -0,0 +1,37 @@
+const normalize = require('../')
+const t = require('tap')
+
+t.test('benign string', async t => {
+  const pkg = { name: 'hello', version: 'world', bin: 'hello.js' }
+  const expect = { name: 'hello', version: 'world', bin: { hello: 'hello.js' } }
+  t.strictSame(normalize(pkg), expect)
+  t.strictSame(normalize(normalize(pkg)), expect, 'double sanitize ok')
+})
+
+t.test('slashy string', async t => {
+  const pkg = { name: 'hello', version: 'world', bin: '/etc/passwd' }
+  const expect = { name: 'hello', version: 'world', bin: { hello: 'etc/passwd' } }
+  t.strictSame(normalize(pkg), expect)
+  t.strictSame(normalize(normalize(pkg)), expect, 'double sanitize ok')
+})
+
+t.test('dotty string', async t => {
+  const pkg = { name: 'hello', version: 'world', bin: '../../../../etc/passwd' }
+  const expect = { name: 'hello', version: 'world', bin: { hello: 'etc/passwd' } }
+  t.strictSame(normalize(pkg), expect)
+  t.strictSame(normalize(normalize(pkg)), expect, 'double sanitize ok')
+})
+
+t.test('double path', async t => {
+  const pkg = { name: 'hello', version: 'world', bin: '/etc/passwd:/bin/usr/exec' }
+  const expect = { name: 'hello', version: 'world', bin: { hello: 'etc/passwd:/bin/usr/exec' } }
+  t.strictSame(normalize(pkg), expect)
+  t.strictSame(normalize(normalize(pkg)), expect, 'double sanitize ok')
+})
+
+t.test('string with no name', async t => {
+  const pkg = { bin: 'foobar.js' }
+  const expect = {}
+  t.strictSame(normalize(pkg), expect)
+  t.strictSame(normalize(normalize(pkg)), expect, 'double sanitize ok')
+})