feat(ui): R3 S2 — loading rows for blank-flash pages, error paths for forever-loading ones

- Blank-flash (showed an empty state on first load before data): DownloadCenter (queue + library
  tabs), AdminUsers (roles + invites), ChatThread, PlaylistsRail now show a loading indicator
  (and an error+retry) instead of a false-empty flash — guarded on `&& !data` so live data isn't
  disturbed on refetch.
- Forever-loading (`isLoading || !data` loops forever on a failed fetch): ConfigPanel, the three
  PlexBrowse subviews (playlist/show/season), and Stats' admin dashboard get an `isError && !data`
  error+retry path before the loading branch.
- Playlists' detail pane already had an error path (isError+retry); its list lives in PlaylistsRail
  (now covered), so no change needed there.

frontend/src/components/AdminUsers.tsx

@@ -7,6 +7,7 @@ import { notify } from "../lib/notifications";
 import { ADMIN_USERS_TAB_KEY } from "../lib/adminUsersTab";
 import Tooltip from "./Tooltip";
 import { Section } from "./ui/form";
+import { StateMessage } from "./QueryState";
 import { useConfirm } from "./ConfirmProvider";
 import Tabs, { usePersistedTab } from "./Tabs";
 import { PageToolbar } from "./PageShell";
@@ -159,7 +160,13 @@ function UsersRoles({ me }: { me: Me }) {
   return (
     <Section card title={t("users.roles.title")}>
       <p className="text-xs text-muted leading-relaxed mb-3">{t("users.roles.intro")}</p>
-      {rows.length === 0 ? (
+      {q.isError && !q.data ? (
+        <StateMessage tone="error" onRetry={() => q.refetch()}>
+          {t("common.loadError")}
+        </StateMessage>
+      ) : q.isLoading && !q.data ? (
+        <p className="text-sm text-muted">{t("common.loading")}</p>
+      ) : rows.length === 0 ? (
         <p className="text-sm text-muted">{t("users.roles.empty")}</p>
       ) : (
         <div className="space-y-1.5">
@@ -307,7 +314,13 @@ function AdminInvites() {
 
   return (
     <Section card title={t("settings.invites.title")}>
-      {pending.length === 0 ? (
+      {invites.isError && !invites.data ? (
+        <StateMessage tone="error" onRetry={() => invites.refetch()}>
+          {t("common.loadError")}
+        </StateMessage>
+      ) : invites.isLoading && !invites.data ? (
+        <p className="text-sm text-muted">{t("common.loading")}</p>
+      ) : pending.length === 0 ? (
         <p className="text-sm text-muted">{t("settings.invites.noPending")}</p>
       ) : (
         <div className="space-y-1.5">

frontend/src/components/ChatThread.tsx

@@ -5,6 +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 { relativeTime } from "../lib/format";
 import { notify } from "../lib/notifications";
 import { partnerPub, POLL_MS, useKeyState } from "../lib/messaging";
@@ -139,7 +140,15 @@ export default function ChatThread({
         style={fade.style}
         className="flex-1 overflow-y-auto no-scrollbar p-3 flex flex-col gap-2"
       >
-        {items.length === 0 ? (
+        {q.isError && !q.data ? (
+          <div className="m-auto">
+            <StateMessage tone="error" onRetry={() => q.refetch()}>
+              {t("common.loadError")}
+            </StateMessage>
+          </div>
+        ) : q.isPending ? (
+          <div className="m-auto text-sm text-muted">{t("common.loading")}</div>
+        ) : items.length === 0 ? (
           <div className="m-auto text-sm text-muted">{t("messages.threadEmpty")}</div>
         ) : (
           items.map((m) => {

frontend/src/components/ConfigPanel.tsx

@@ -6,6 +6,7 @@ import { api, type ConfigItem, type PlexTestResult } from "../lib/api";
 import { notify } from "../lib/notifications";
 import Tooltip from "./Tooltip";
 import Tabs, { usePersistedTab } from "./Tabs";
+import { StateMessage } from "./QueryState";
 import { PageToolbar } from "./PageShell";
 import { Switch } from "./ui/form";
 import { DraftSaveBar, type SaveState } from "./ui/DraftSaveBar";
@@ -148,6 +149,13 @@ export default function ConfigPanel() {
     setDraft((d) => ({ ...d, plex_libraries: next.join(",") }));
   };
 
+  if (q.isError && !data) {
+    return (
+      <StateMessage tone="error" onRetry={() => q.refetch()}>
+        {t("common.loadError")}
+      </StateMessage>
+    );
+  }
   if (q.isLoading || !data) {
     return <div className="p-4 max-w-3xl mx-auto text-muted">{t("config.loading")}</div>;
   }

frontend/src/components/DownloadCenter.tsx

@@ -19,6 +19,7 @@ import {
 import clsx from "clsx";
 import Tabs, { usePersistedTab } from "./Tabs";
 import { PageToolbar } from "./PageShell";
+import { 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).
@@ -803,11 +804,18 @@ export default function DownloadCenter() {
                   </IconBtn>
                 </DownloadRow>
               ))}
-              {queue.length === 0 && (
-                <div className="text-sm text-muted py-10 text-center">
-                  {t("downloads.empty.queue")}
-                </div>
-              )}
+              {queue.length === 0 &&
+                (jobsQ.isError && !jobsQ.data ? (
+                  <StateMessage tone="error" onRetry={() => jobsQ.refetch()}>
+                    {t("common.loadError")}
+                  </StateMessage>
+                ) : jobsQ.isLoading ? (
+                  <div className="text-sm text-muted py-10 text-center">{t("common.loading")}</div>
+                ) : (
+                  <div className="text-sm text-muted py-10 text-center">
+                    {t("downloads.empty.queue")}
+                  </div>
+                ))}
             </div>
           </>
         )}
@@ -860,11 +868,18 @@ export default function DownloadCenter() {
                   </IconBtn>
                 </DownloadRow>
               ))}
-              {library.length === 0 && (
-                <div className="text-sm text-muted py-10 text-center">
-                  {t("downloads.empty.done")}
-                </div>
-              )}
+              {library.length === 0 &&
+                (jobsQ.isError && !jobsQ.data ? (
+                  <StateMessage tone="error" onRetry={() => jobsQ.refetch()}>
+                    {t("common.loadError")}
+                  </StateMessage>
+                ) : jobsQ.isLoading ? (
+                  <div className="text-sm text-muted py-10 text-center">{t("common.loading")}</div>
+                ) : (
+                  <div className="text-sm text-muted py-10 text-center">
+                    {t("downloads.empty.done")}
+                  </div>
+                ))}
             </div>
           </>
         )}

frontend/src/components/PlaylistsRail.tsx

@@ -210,9 +210,20 @@ export default function PlaylistsRail({
       title: t("playlists.listGroup"),
       body: (
         <>
-          {playlists.length === 0 && !listQuery.isLoading && (
-            <div className="text-xs text-muted px-1 py-1">{t("playlists.noneYet")}</div>
-          )}
+          {playlists.length === 0 &&
+            (listQuery.isError && !listQuery.data ? (
+              <button
+                type="button"
+                onClick={() => listQuery.refetch()}
+                className="text-xs text-red-400 px-1 py-1 text-left hover:underline"
+              >
+                {t("common.loadError")} — {t("common.retry")}
+              </button>
+            ) : listQuery.isLoading ? (
+              <div className="text-xs text-muted px-1 py-1">{t("common.loading")}</div>
+            ) : (
+              <div className="text-xs text-muted px-1 py-1">{t("playlists.noneYet")}</div>
+            ))}
           {playlists.length > 0 && visiblePlaylists.length === 0 && (
             <div className="text-xs text-muted px-1 py-1">{t("playlists.noMatches")}</div>
           )}

frontend/src/components/PlexBrowse.tsx

@@ -599,7 +599,11 @@ function PlexInfoView({
           {t("plex.backToLibrary")}
         </button>
       </div>
-      {q.isLoading || !q.data ? (
+      {q.isError && !q.data ? (
+        <StateMessage tone="error" onRetry={() => q.refetch()}>
+          {t("common.loadError")}
+        </StateMessage>
+      ) : q.isLoading || !q.data ? (
         <p className="p-8 text-muted text-sm">{t("plex.loading")}</p>
       ) : (
         <Suspense fallback={<p className="p-8 text-muted text-sm">{t("plex.loading")}</p>}>
@@ -1018,7 +1022,11 @@ function PlexShowView({
     <div className="p-4 max-w-[1200px] mx-auto glass-media">
       <BackBtn onBack={onBack} label={t("plex.backToLibrary")} />
 
-      {q.isLoading || !d || !show ? (
+      {q.isError && !q.data ? (
+        <StateMessage tone="error" onRetry={() => q.refetch()}>
+          {t("common.loadError")}
+        </StateMessage>
+      ) : q.isLoading || !d || !show ? (
         <p className="text-muted text-sm">{t("plex.loading")}</p>
       ) : (
         <>
@@ -1250,7 +1258,11 @@ function PlexSeasonView({
     <div className="p-4 max-w-[1200px] mx-auto glass-media">
       <BackBtn onBack={onBack} label={t("plex.series.backToShow")} />
 
-      {q.isLoading || !d || !se ? (
+      {q.isError && !q.data ? (
+        <StateMessage tone="error" onRetry={() => q.refetch()}>
+          {t("common.loadError")}
+        </StateMessage>
+      ) : q.isLoading || !d || !se ? (
         <p className="text-muted text-sm">{t("plex.loading")}</p>
       ) : (
         <>

frontend/src/components/Stats.tsx

@@ -247,7 +247,11 @@ function SystemStats() {
         {t("stats.introAfter")}
       </p>
 
-      {q.isLoading ? (
+      {q.isError && !data ? (
+        <StateMessage tone="error" onRetry={() => q.refetch()}>
+          {t("common.loadError")}
+        </StateMessage>
+      ) : q.isLoading ? (
         <div className="text-muted py-8">{t("stats.loading")}</div>
       ) : !data ? (
         <div className="text-muted py-8">{t("stats.noData")}</div>