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/DownloadCenter.tsx

@@ -19,7 +19,7 @@ import {
 import clsx from "clsx";
 import Tabs, { usePersistedTab } from "./Tabs";
 import { PageToolbar } from "./PageShell";
-import { StateMessage } from "./QueryState";
+import { LoadingState, StateMessage } from "./QueryState";
 import Modal from "./Modal";
 // Lazy: these dialogs/editors open on demand, so they stay out of the Downloads page chunk until
 // used (the video editor in particular is heavy — filmstrip + scrubber).
@@ -810,7 +810,7 @@ export default function DownloadCenter() {
                     {t("common.loadError")}
                   </StateMessage>
                 ) : jobsQ.isLoading ? (
-                  <div className="text-sm text-muted py-10 text-center">{t("common.loading")}</div>
+                  <LoadingState />
                 ) : (
                   <div className="text-sm text-muted py-10 text-center">
                     {t("downloads.empty.queue")}
@@ -874,7 +874,7 @@ export default function DownloadCenter() {
                     {t("common.loadError")}
                   </StateMessage>
                 ) : jobsQ.isLoading ? (
-                  <div className="text-sm text-muted py-10 text-center">{t("common.loading")}</div>
+                  <LoadingState />
                 ) : (
                   <div className="text-sm text-muted py-10 text-center">
                     {t("downloads.empty.done")}