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/config/flat/errors.js

@@ -0,0 +1,14 @@
+/**
+ * unopinionated config. just the things that are necessarily runtime errors
+ * waiting to happen.
+ * @type {Object}
+ */
+module.exports = {
+  rules: {
+    'import/no-unresolved': 2,
+    'import/named': 2,
+    'import/namespace': 2,
+    'import/default': 2,
+    'import/export': 2,
+  },
+};

node_modules/eslint-plugin-import/config/flat/react.js

@@ -0,0 +1,19 @@
+/**
+ * Adds `.jsx` as an extension, and enables JSX parsing.
+ *
+ * Even if _you_ aren't using JSX (or .jsx) directly, if your dependencies
+ * define jsnext:main and have JSX internally, you may run into problems
+ * if you don't enable these settings at the top level.
+ */
+module.exports = {
+  settings: {
+    'import/extensions': ['.js', '.jsx', '.mjs', '.cjs'],
+  },
+  languageOptions: {
+    parserOptions: {
+      ecmaFeatures: {
+        jsx: true,
+      },
+    },
+  },
+};

node_modules/eslint-plugin-import/config/flat/recommended.js

@@ -0,0 +1,26 @@
+/**
+ * The basics.
+ * @type {Object}
+ */
+module.exports = {
+  rules: {
+    // analysis/correctness
+    'import/no-unresolved': 'error',
+    'import/named': 'error',
+    'import/namespace': 'error',
+    'import/default': 'error',
+    'import/export': 'error',
+
+    // red flags (thus, warnings)
+    'import/no-named-as-default': 'warn',
+    'import/no-named-as-default-member': 'warn',
+    'import/no-duplicates': 'warn',
+  },
+
+  // need all these for parsing dependencies (even if _your_ code doesn't need
+  // all of them)
+  languageOptions: {
+    ecmaVersion: 2018,
+    sourceType: 'module',
+  },
+};

node_modules/eslint-plugin-import/config/flat/warnings.js

@@ -0,0 +1,11 @@
+/**
+ * more opinionated config.
+ * @type {Object}
+ */
+module.exports = {
+  rules: {
+    'import/no-named-as-default': 1,
+    'import/no-named-as-default-member': 1,
+    'import/no-duplicates': 1,
+  },
+};