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/nth-check/lib/parse.d.ts

@@ -0,0 +1,9 @@
+/**
+ * Parses an expression.
+ *
+ * @throws An `Error` if parsing fails.
+ * @returns An array containing the integer step size and the integer offset of the nth rule.
+ * @example nthCheck.parse("2n+3"); // returns [2, 3]
+ */
+export declare function parse(formula: string): [a: number, b: number];
+//# sourceMappingURL=parse.d.ts.map