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/stats/StatsPage.tsx

@@ -8,6 +8,7 @@ import { cn } from "@/lib/cn";
 import { formatBytes } from "@/lib/format";
 import type { StatJob, SystemStats } from "@/lib/types";
 import { useAuth } from "@/store/auth";
+import { toast } from "@/store/toasts";
 
 const REFRESH_MS = 2000;
 
@@ -82,13 +83,11 @@ function JobRow({
   showSummary,
   onCancel,
   cancelling,
-  cancelError,
 }: {
   job: StatJob;
   showSummary?: boolean;
   onCancel?: () => void;
   cancelling?: boolean;
-  cancelError?: string | null;
 }) {
   const Icon = job.kind === "download" ? Download : ScanSearch;
   return (
@@ -111,9 +110,6 @@ function JobRow({
           </button>
         ) : null}
       </div>
-      {cancelError ? (
-        <p className="pl-5 text-[11px] text-ctp-red">{cancelError}</p>
-      ) : null}
       {showSummary ? (
         <p className="truncate pl-5 text-[11px] text-ctp-overlay0" title={job.summary ?? job.detail}>
           {job.summary ?? job.detail}
@@ -159,10 +155,13 @@ export default function StatsPage() {
           : `/api/matches/${job.id}/cancel/`,
         { method: "POST" },
       ),
-    onSuccess: () => {
+    onSuccess: (_data, job) => {
       void queryClient.invalidateQueries({ queryKey: ["stats"] });
       void queryClient.invalidateQueries({ queryKey: ["status"] });
+      toast.ok(`Cancelled ${job.label}.`);
     },
+    onError: (error, job) =>
+      toast.error(`Could not cancel ${job.label}: ${errorMessage(error)}`),
   });
   const [autoScroll, setAutoScroll] = useState(true);
   const logRef = useRef<HTMLDivElement>(null);
@@ -369,12 +368,6 @@ export default function StatsPage() {
                     cancelMutation.isPending &&
                     cancelMutation.variables?.id === job.id
                   }
-                  cancelError={
-                    cancelMutation.isError &&
-                    cancelMutation.variables?.id === job.id
-                      ? errorMessage(cancelMutation.error)
-                      : null
-                  }
                 />
               ))}
             </ul>