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/ChatThread.tsx

@@ -5,7 +5,7 @@ import { Send } from "lucide-react";
 import { api, HttpError, type Message, type MessageUser } from "../lib/api";
 import { useLiveQuery } from "../lib/useLiveQuery";
 import { useScrollFade } from "../lib/useScrollFade";
-import { StateMessage } from "./QueryState";
+import { LoadingState, StateMessage } from "./QueryState";
 import { relativeTime } from "../lib/format";
 import { notify } from "../lib/notifications";
 import { partnerPub, POLL_MS, useKeyState } from "../lib/messaging";
@@ -147,7 +147,9 @@ export default function ChatThread({
             </StateMessage>
           </div>
         ) : q.isPending ? (
-          <div className="m-auto text-sm text-muted">{t("common.loading")}</div>
+          <div className="m-auto">
+            <LoadingState />
+          </div>
         ) : items.length === 0 ? (
           <div className="m-auto text-sm text-muted">{t("messages.threadEmpty")}</div>
         ) : (