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/Feed.tsx

@@ -36,7 +36,7 @@ import {
 import { FEED_VIEWS, type FeedView } from "../lib/feedView";
 import { clearedFilters, useActiveFilters } from "../lib/useActiveFilters";
 import ActiveFilterChips from "./ActiveFilterChips";
-import { StateMessage } from "./QueryState";
+import { LoadingState, StateMessage } from "./QueryState";
 import { PageToolbar } from "./PageShell";
 import { useWizard } from "./WizardProvider";
 import ViewSwitcher from "./ViewSwitcher";
@@ -493,7 +493,7 @@ export default function Feed({
     );
   }
 
-  if (query.isLoading) return <div className="p-8 text-muted">{t("feed.loading")}</div>;
+  if (query.isLoading) return <LoadingState label={t("feed.loading")} />;
   if (query.isError && !query.data)
     return (
       <StateMessage tone="error" onRetry={() => query.refetch()}>