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/ChannelDiscovery.tsx

@@ -15,7 +15,7 @@ import ChannelLink from "./ChannelLink";
 import AboutCell from "./AboutCell";
 import DataTable, { type Column } from "./DataTable";
 import ChannelLayoutGrid from "./ChannelLayoutGrid";
-import { StateMessage } from "./QueryState";
+import { LoadingState, StateMessage } from "./QueryState";
 import ColumnSortControl from "./ColumnSortControl";
 import Pager from "./Pager";
 import { PageToolbar } from "./PageShell";
@@ -229,7 +229,7 @@ export default function ChannelDiscovery({
             {t("common.loadError")}
           </StateMessage>
         ) : query.isLoading ? (
-          <div className="text-muted py-8">{t("channels.discovery.loading")}</div>
+          <LoadingState label={t("channels.discovery.loading")} />
         ) : layout === "table" ? (
           <DataTable
             rows={rows}