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/eslint-plugin-import/docs/rules/no-dynamic-require.md

@@ -0,0 +1,25 @@
+# import/no-dynamic-require
+
+<!-- end auto-generated rule header -->
+
+The `require` method from CommonJS is used to import modules from different files. Unlike the ES6 `import` syntax, it can be given expressions that will be resolved at runtime. While this is sometimes necessary and useful, in most cases it isn't. Using expressions (for instance, concatenating a path and variable) as the argument makes it harder for tools to do static code analysis, or to find where in the codebase a module is used.
+
+This rule forbids every call to `require()` that uses expressions for the module name argument.
+
+## Rule Details
+
+### Fail
+
+```js
+require(name);
+require('../' + name);
+require(`../${name}`);
+require(name());
+```
+
+### Pass
+
+```js
+require('../name');
+require(`../name`);
+```