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/sirv/sirv.d.ts

@@ -0,0 +1,25 @@
+declare module 'sirv' {
+	import type { Stats } from 'fs';
+	import type { IncomingMessage, ServerResponse } from 'http';
+
+	type Arrayable<T> = T | T[];
+	export type NextHandler = () => void | Promise<void>;
+	export type RequestHandler = (req: IncomingMessage, res: ServerResponse, next?: NextHandler) => void;
+
+	export interface Options {
+		dev?: boolean;
+		etag?: boolean;
+		maxAge?: number;
+		immutable?: boolean;
+		single?: string | boolean;
+		ignores?: false | Arrayable<string | RegExp>;
+		extensions?: string[];
+		dotfiles?: boolean;
+		brotli?: boolean;
+		gzip?: boolean;
+		onNoMatch?: (req: IncomingMessage, res: ServerResponse) => void;
+		setHeaders?: (res: ServerResponse, pathname: string, stats: Stats) => void;
+	}
+
+	export default function(dir?: string, opts?: Options): RequestHandler;
+}