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/resolve/test/resolver/nested_symlinks/mylib/async.js

@@ -0,0 +1,26 @@
+var a = require.resolve('buffer/').replace(process.cwd(), '$CWD');
+var b;
+var c;
+
+function test() {
+    console.log(a, ': require.resolve, preserveSymlinks ' + (process.execArgv.indexOf('preserve-symlinks') > -1 ? 'true' : 'false'));
+    console.log(b, ': preserveSymlinks true');
+    console.log(c, ': preserveSymlinks false');
+
+    if (a !== b && a !== c) {
+        throw 'async: no match';
+    }
+    console.log('async: success! a matched either b or c\n');
+}
+
+require('resolve')('buffer/', { preserveSymlinks: true }, function (err, result) {
+    if (err) { throw err; }
+    b = result.replace(process.cwd(), '$CWD');
+    if (b && c) { test(); }
+});
+require('resolve')('buffer/', { preserveSymlinks: false }, function (err, result) {
+    if (err) { throw err; }
+    c = result.replace(process.cwd(), '$CWD');
+    if (b && c) { test(); }
+});
+

node_modules/resolve/test/resolver/nested_symlinks/mylib/package.json

@@ -0,0 +1,15 @@
+{
+  "name": "mylib",
+  "version": "0.0.0",
+  "description": "",
+  "private": true,
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "keywords": [],
+  "author": "",
+  "license": "ISC",
+  "dependencies": {
+    "buffer": "*"
+  }
+}

node_modules/resolve/test/resolver/nested_symlinks/mylib/sync.js

@@ -0,0 +1,12 @@
+var a = require.resolve('buffer/').replace(process.cwd(), '$CWD');
+var b = require('resolve').sync('buffer/', { preserveSymlinks: true }).replace(process.cwd(), '$CWD');
+var c = require('resolve').sync('buffer/', { preserveSymlinks: false }).replace(process.cwd(), '$CWD');
+
+console.log(a, ': require.resolve, preserveSymlinks ' + (process.execArgv.indexOf('preserve-symlinks') > -1 ? 'true' : 'false'));
+console.log(b, ': preserveSymlinks true');
+console.log(c, ': preserveSymlinks false');
+
+if (a !== b && a !== c) {
+    throw 'sync: no match';
+}
+console.log('sync: success! a matched either b or c\n');