Toast action results and confirm destructive actions in one dialog

Inline banners and per-row status text reported action results all over
the app; they are replaced by a small toast stack (bottom-right, Level 3
floating well styling) that only speaks for actions: successes fade,
errors stay until dismissed, and form-field validation stays inline.

Destructive actions no longer use bespoke inline confirm steps (the
library detail's Confirm delete button) or fire immediately (duplicate
copies/items, delete page selections, temp cleanup, upload discard, job
cancellation): they all go through one promise-based confirm dialog
(confirmAction) with a danger variant, Escape/backdrop to cancel.

frontend/src/features/users/UsersPage.tsx

@@ -7,6 +7,7 @@ import { cn } from "@/lib/cn";
 import { formatDate } from "@/lib/format";
 import type { AdminUser, Paginated } from "@/lib/types";
 import { useAuth } from "@/store/auth";
+import { toast } from "@/store/toasts";
 
 const ROLE_OPTIONS = [
   { value: "user", label: "User" },
@@ -17,8 +18,6 @@ const ROLE_OPTIONS = [
 function UserRow({ profile }: { profile: AdminUser }) {
   const queryClient = useQueryClient();
   const [avatarJId, setAvatarJId] = useState(profile.avatar_j_id ?? "");
-  const [message, setMessage] = useState<string | null>(null);
-  const [error, setError] = useState<string | null>(null);
 
   const mutation = useMutation({
     mutationFn: (payload: Record<string, string | null>) =>
@@ -27,15 +26,11 @@ function UserRow({ profile }: { profile: AdminUser }) {
         json: payload,
       }),
     onSuccess: (updated) => {
-      setMessage("Saved.");
-      setError(null);
       setAvatarJId(updated.avatar_j_id ?? "");
       void queryClient.invalidateQueries({ queryKey: ["users"] });
+      toast.ok(`Saved ${updated.username}.`);
     },
-    onError: (err) => {
-      setError(errorMessage(err));
-      setMessage(null);
-    },
+    onError: (err) => toast.error(errorMessage(err)),
   });
 
   return (
@@ -105,13 +100,6 @@ function UserRow({ profile }: { profile: AdminUser }) {
           Save avatar
         </Button>
       </div>
-
-      {message ? (
-        <p className="text-xs text-ctp-green lg:w-20">{message}</p>
-      ) : null}
-      {error ? (
-        <p className="text-xs text-ctp-red lg:w-40">{error}</p>
-      ) : null}
     </div>
   );
 }