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/bare-url/lib/url-search-params.d.ts

@@ -0,0 +1,23 @@
+interface URLSearchParams extends Iterable<[name: string, value: string]> {
+  readonly size: number
+
+  append(name: string, value: string): void
+  delete(name: string, value?: string): void
+  get(name: string): string | undefined
+  getAll(name: string): string[]
+  has(name: string, value?: string): boolean
+  set(name: string, value: string): void
+
+  toString(): string
+  toJSON(): string
+}
+
+declare class URLSearchParams {
+  constructor(init: string | Record<string, string> | Iterable<[string, string]>)
+}
+
+declare namespace URLSearchParams {
+  export function isURLSearchParams(value: unknown): value is URLSearchParams
+}
+
+export = URLSearchParams