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/string_decoder/README.md

@@ -0,0 +1,47 @@
+# string_decoder
+
+***Node-core v8.9.4 string_decoder for userland***
+
+
+[![NPM](https://nodei.co/npm/string_decoder.png?downloads=true&downloadRank=true)](https://nodei.co/npm/string_decoder/)
+[![NPM](https://nodei.co/npm-dl/string_decoder.png?&months=6&height=3)](https://nodei.co/npm/string_decoder/)
+
+
+```bash
+npm install --save string_decoder
+```
+
+***Node-core string_decoder for userland***
+
+This package is a mirror of the string_decoder implementation in Node-core.
+
+Full documentation may be found on the [Node.js website](https://nodejs.org/dist/v8.9.4/docs/api/).
+
+As of version 1.0.0 **string_decoder** uses semantic versioning.
+
+## Previous versions
+
+Previous version numbers match the versions found in Node core, e.g. 0.10.24 matches Node 0.10.24, likewise 0.11.10 matches Node 0.11.10.
+
+## Update
+
+The *build/* directory contains a build script that will scrape the source from the [nodejs/node](https://github.com/nodejs/node) repo given a specific Node version.
+
+## Streams Working Group
+
+`string_decoder` is maintained by the Streams Working Group, which
+oversees the development and maintenance of the Streams API within
+Node.js. The responsibilities of the Streams Working Group include:
+
+* Addressing stream issues on the Node.js issue tracker.
+* Authoring and editing stream documentation within the Node.js project.
+* Reviewing changes to stream subclasses within the Node.js project.
+* Redirecting changes to streams from the Node.js project to this
+  project.
+* Assisting in the implementation of stream providers within Node.js.
+* Recommending versions of `readable-stream` to be included in Node.js.
+* Messaging about the future of streams to give the community advance
+  notice of changes.
+
+See [readable-stream](https://github.com/nodejs/readable-stream) for
+more details.