fix(mui): restore distinct create/edit submit labels on Users modal

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/admin/pages/Users.tsx

@@ -381,6 +381,7 @@ export default function Users() {
         onSubmit={handleSubmit}
         title={editingUser ? "Upravit uživatele" : "Přidat nového uživatele"}
         loading={saving}
+        submitText={editingUser ? "Uložit změny" : "Vytvořit uživatele"}
       >
         <Box sx={{ display: "flex", gap: 2, flexWrap: "wrap" }}>
           <Box sx={{ flex: "1 1 200px" }}>