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/Channels.tsx

@@ -28,7 +28,7 @@ import { notify } from "../lib/notifications";
 import Tooltip from "./Tooltip";
 import DataTable, { type Column } from "./DataTable";
 import ChannelLayoutGrid from "./ChannelLayoutGrid";
-import { StateMessage } from "./QueryState";
+import { LoadingState, StateMessage } from "./QueryState";
 import Overlay from "./Overlay";
 import ViewSwitcher, { type ViewOption } from "./ViewSwitcher";
 import ColumnSortControl from "./ColumnSortControl";
@@ -715,7 +715,7 @@ export default function Channels() {
               {t("common.loadError")}
             </StateMessage>
           ) : channelsQuery.isLoading ? (
-            <div className="text-muted py-8">{t("channels.loading")}</div>
+            <LoadingState label={t("channels.loading")} />
           ) : layout === "table" ? (
             <DataTable
               rows={visibleChannels}