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/json-stable-stringify-without-jsonify/example/key_cmp.js

@@ -0,0 +1,7 @@
+var stringify = require('../');
+
+var obj = { c: 8, b: [{z:6,y:5,x:4},7], a: 3 };
+var s = stringify(obj, function (a, b) {
+    return a.key < b.key ? 1 : -1;
+});
+console.log(s);

node_modules/json-stable-stringify-without-jsonify/example/nested.js

@@ -0,0 +1,3 @@
+var stringify = require('../');
+var obj = { c: 8, b: [{z:6,y:5,x:4},7], a: 3 };
+console.log(stringify(obj));

node_modules/json-stable-stringify-without-jsonify/example/str.js

@@ -0,0 +1,3 @@
+var stringify = require('../');
+var obj = { c: 6, b: [4,5], a: 3 };
+console.log(stringify(obj));

node_modules/json-stable-stringify-without-jsonify/example/value_cmp.js

@@ -0,0 +1,7 @@
+var stringify = require('../');
+
+var obj = { d: 6, c: 5, b: [{z:3,y:2,x:1},9], a: 10 };
+var s = stringify(obj, function (a, b) {
+    return a.value < b.value ? 1 : -1;
+});
+console.log(s);