feat(product): trigger product list refresh on product creation event

frontend/app/admin/products/AdminProductList.tsx

@@ -69,6 +69,12 @@ export default function AdminProductList() {
     refetchProducts();
   }, [refetchProducts]);
 
+  useEffect(() => {
+    const handler = () => refetchProducts();
+    window.addEventListener('product-created', handler);
+    return () => window.removeEventListener('product-created', handler);
+  }, [refetchProducts]);
+
   useEffect(() => {
     fetch('/api/categories')
       .then((r) => r.json())

frontend/app/inventory/ProductForm.tsx

@@ -1,12 +1,10 @@
 'use client';
 
 import { useState } from 'react';
-import { useRouter } from 'next/navigation';
 
 export default function ProductForm() {
   const [isPending, setIsPending] = useState(false);
   const [error, setError] = useState<string | null>(null);
-  const router = useRouter();
 
   return (
     <form
@@ -29,7 +27,7 @@ export default function ProductForm() {
             throw new Error(data?.error || 'Kunde inte skapa produkt');
           }
           form.reset();
-          router.refresh();
+          window.dispatchEvent(new CustomEvent('product-created'));
         } catch (err) {
           setError(err instanceof Error ? err.message : 'Okänt fel');
         } finally {