feat(ux): R11 feedback symmetry — Plex/download/rollback/deny notices

Give equal-weight actions equal-weight feedback (R11).

S1 Plex error toasts: the watched-toggles (card / season mark-all / episode /
info-panel / show mark-all) used to fail silently on 403/404/429; each now surfaces
the server reason via a shared notifyActionError() + resyncs the optimistic flip.
The playback auto-mark-watched stays intentionally silent (a mid-play toast is
noise; the next sync corrects it). New generic lib/actionErrors.ts (Plex + saved
views reuse it; notifyYouTubeActionError delegates its non-403 case to it).

S2 download-done inbox notification: worker.py emits a best-effort type=download_done
notice to the job owner on real completion (regular + edit jobs, not instant
cache-hits), rendered/localized in the inbox with an Open-Downloads link.

S3 optimistic rollbacks: SavedViewsWidget create/rename/toggle-default/remove/reorder
and the inbox revert-state no longer swallow failures — they toast + refetch to
resync (the reorder's optimistic order reverts to server truth).

S4 access-request deny: deny_invite now emails the requester (send_access_denied),
mirroring approve — no more silent limbo.

frontend/src/components/NotificationsPanel.tsx

@@ -8,6 +8,7 @@ import {
   Bell,
   Check,
   CheckCheck,
+  Download,
   ExternalLink,
   Eye,
   RotateCcw,
@@ -18,6 +19,7 @@ import {
   X,
 } from "lucide-react";
 import { api, type AppNotification } from "../lib/api";
+import { notifyActionError } from "../lib/actionErrors";
 import { useLiveQuery } from "../lib/useLiveQuery";
 import { focusAccessRequestsTab } from "../lib/adminUsersTab";
 import {
@@ -114,7 +116,7 @@ export default function NotificationsPanel() {
         // Quietly resolve the now-stale notice (no confirmation toast — the change is visible).
         resolveVideo(meta.videoId);
       })
-      .catch(() => {});
+      .catch((e) => notifyActionError(e, t("inbox.revertFailed")));
   }
 
   return (
@@ -180,6 +182,7 @@ export default function NotificationsPanel() {
                       onRead={() => readMut.mutate(n.id)}
                       onDismiss={() => dismissMut.mutate(n.id)}
                       onOpenScheduler={() => setPage("scheduler")}
+                      onOpenDownloads={() => setPage("downloads")}
                     />
                   ))}
                 </div>
@@ -222,12 +225,14 @@ function NotificationRow({
   onRead,
   onDismiss,
   onOpenScheduler,
+  onOpenDownloads,
 }: {
   n: AppNotification;
   t: TFunction;
   onRead: () => void;
   onDismiss: () => void;
   onOpenScheduler: () => void;
+  onOpenDownloads: () => void;
 }) {
   // The maintenance producer ships the affected videos in `data.videos`; list a few titles.
   const videos: { id: string; title: string | null }[] = Array.isArray(n.data?.videos)
@@ -237,6 +242,7 @@ function NotificationRow({
   // payload; the server-stored title/body are an English fallback for any unknown type.
   const isMaintenance = n.type === "maintenance" && typeof n.data?.count === "number";
   const isScheduler = n.type === "scheduler" && typeof n.data?.job_id === "string";
+  const isDownloadDone = n.type === "download_done";
   let title = n.title;
   let body = n.body;
   if (isMaintenance) {
@@ -252,6 +258,11 @@ function NotificationRow({
       job,
     });
     body = d.summary || n.body;
+  } else if (isDownloadDone) {
+    // "Download ready", with the video's title as the body (the producer ships it in data.title).
+    const d = n.data as { title?: string | null };
+    title = t("inbox.downloadDone.title");
+    body = d.title || n.body;
   }
   return (
     <div
@@ -289,6 +300,15 @@ function NotificationRow({
             {t("inbox.openScheduler")}
           </button>
         )}
+        {isDownloadDone && (
+          <button
+            onClick={onOpenDownloads}
+            className="flex items-center gap-1 text-accent text-sm font-semibold hover:underline mt-1.5"
+          >
+            <Download className="w-3.5 h-3.5" />
+            {t("inbox.openDownloads")}
+          </button>
+        )}
       </div>
       <div className="flex items-center gap-1 shrink-0">
         {!n.read && (