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/NotificationsPanel.tsx

@@ -35,7 +35,7 @@ import {
 import { channelYouTubeUrl, relativeFromMs, relativeTime } from "../lib/format";
 import { LEVEL_STYLE } from "./Toaster";
 import { PageToolbar } from "./PageShell";
-import { StateMessage } from "./QueryState";
+import { LoadingState, StateMessage } from "./QueryState";
 import { useNavigationActions } from "./NavigationProvider";
 import { useChannelsActions } from "./ChannelsProvider";
 import { useFeedFilters, useFeedFiltersActions } from "./FeedFiltersProvider";
@@ -156,7 +156,7 @@ export default function NotificationsPanel() {
             {t("common.loadError")}
           </StateMessage>
         ) : q.isLoading && !q.data && clientItems.length === 0 ? (
-          <div className="p-8 text-muted text-center">{t("common.loading")}</div>
+          <LoadingState />
         ) : !hasAny ? (
           <div className="glass rounded-2xl p-10 text-center text-muted">
             <Bell className="w-8 h-8 mx-auto mb-3 opacity-40" />