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/@sentry/node/esm/flags.js

@@ -0,0 +1,16 @@
+/*
+ * This file defines flags and constants that can be modified during compile time in order to facilitate tree shaking
+ * for users.
+ *
+ * Debug flags need to be declared in each package individually and must not be imported across package boundaries,
+ * because some build tools have trouble tree-shaking imported guards.
+ *
+ * As a convention, we define debug flags in a `flags.ts` file in the root of a package's `src` folder.
+ *
+ * Debug flag files will contain "magic strings" like `__SENTRY_DEBUG__` that may get replaced with actual values during
+ * our, or the user's build process. Take care when introducing new flags - they must not throw if they are not
+ * replaced.
+ */
+/** Flag that is true for debug builds, false otherwise. */
+export var IS_DEBUG_BUILD = typeof __SENTRY_DEBUG__ === 'undefined' ? true : __SENTRY_DEBUG__;
+//# sourceMappingURL=flags.js.map