feat(ui): shared LoadingState — a centered accent spinner instead of plain loading text

Replaces the plain "Loading…" text in every R3 loading branch with a single shared LoadingState
(a spinning lucide Loader2 in the accent colour + label, centered, role=status/aria-live) — one
component so all loads read the same and can be swapped for skeletons later in one place. Applied
across Feed, Channels, ChannelDiscovery, AuditLog, NotificationsPanel, Messages, Scheduler, Stats,
PlexBrowse (grid + subviews), PlexPlaylistView, ConfigPanel, DownloadCenter, AdminUsers, ChatThread.
Left the small "load more" footer and lazy Suspense fallbacks as-is.

frontend/src/components/PlexPlaylistView.tsx

@@ -33,7 +33,7 @@ import {
 import { api, type PlexCard } from "../lib/api";
 import { getAccountRaw, LS, setAccountRaw } from "../lib/storage";
 import { useConfirm } from "./ConfirmProvider";
-import { StateMessage } from "./QueryState";
+import { LoadingState, StateMessage } from "./QueryState";
 
 // A playlist's items, grouped for readability: movies stay standalone, while a run of episodes from the
 // same show collapses into a season/show group so a whole series doesn't sprawl into an endless flat
@@ -582,7 +582,7 @@ export default function PlexPlaylistView({
             {t("common.loadError")}
           </StateMessage>
         ) : q.isLoading ? (
-          <p className="py-6 text-center text-sm text-muted">{t("plex.loading")}</p>
+          <LoadingState label={t("plex.loading")} />
         ) : items.length === 0 ? (
           <p className="py-6 text-center text-sm text-muted">{t("plex.playlist.empty")}</p>
         ) : (