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/http-proxy-agent/dist/agent.d.ts

@@ -0,0 +1,32 @@
+/// <reference types="node" />
+import net from 'net';
+import { Agent, ClientRequest, RequestOptions } from 'agent-base';
+import { HttpProxyAgentOptions } from '.';
+interface HttpProxyAgentClientRequest extends ClientRequest {
+    path: string;
+    output?: string[];
+    outputData?: {
+        data: string;
+    }[];
+    _header?: string | null;
+    _implicitHeader(): void;
+}
+/**
+ * The `HttpProxyAgent` implements an HTTP Agent subclass that connects
+ * to the specified "HTTP proxy server" in order to proxy HTTP requests.
+ *
+ * @api public
+ */
+export default class HttpProxyAgent extends Agent {
+    private secureProxy;
+    private proxy;
+    constructor(_opts: string | HttpProxyAgentOptions);
+    /**
+     * Called when the node-core HTTP client library is creating a
+     * new HTTP request.
+     *
+     * @api protected
+     */
+    callback(req: HttpProxyAgentClientRequest, opts: RequestOptions): Promise<net.Socket>;
+}
+export {};