refactor(fe): migrate plex/messaging/admin/downloads/notifications to qk (R7 S2b)

Extend lib/queryKeys.ts to the remaining ~34 key roots and migrate every
remaining literal (queryKey: [...] AND the positional useLiveQuery keys) in
36 files. All ~200 React Query keys across the app now route through the
factory; zero raw key literals remain outside queryKeys.ts.

The heterogeneous composite plex keys (plex-library/facets/collections/
playlists carry a filters object, a ratingKeys array, or a union/group
discriminator) take a variadic pass-through — the factory centralizes the
ROOT string; single-id keys stay precisely typed. Nullable keys (thread,
playlist, ytSearch) accept null so a null segment is preserved.

Pure substitution — byte-identical key arrays, so TanStack prefix matching
is unchanged. Gate green: typecheck (app+node+e2e), eslint (0 err),
prettier, 68 vitest. Runtime-verified on a fresh dev server: Feed + Plex
modules load, feed/facets/tags/my-status/plex-library/plex-facets/
plex-collections/plex-playlists all 200, full UI renders.

frontend/src/components/WizardProvider.tsx

@@ -9,6 +9,7 @@ import {
   useState,
   type ReactNode,
 } from "react";
+import { qk } from "../lib/queryKeys";
 import { useQuery } from "@tanstack/react-query";
 import { api } from "../lib/api";
 import { shouldAutoOpenOnboarding } from "../lib/onboarding";
@@ -21,7 +22,7 @@ const OnboardingWizard = lazy(() => import("./OnboardingWizard"));
 //
 // The wizard auto-opens on first login for accounts that still need to connect YouTube (derived from
 // granted scopes + storage flags, so it's stable across the OAuth round-trip) and is reopenable from
-// Settings / the notify "reconnect" action. It reads `me` as a passive ["me"] observer (App owns the
+// Settings / the notify "reconnect" action. It reads `me` as a passive qk.me() observer (App owns the
 // fetching query), so it re-runs the auto-open check when the account resolves or its grants change.
 
 interface WizardActions {
@@ -43,7 +44,7 @@ export function useWizard(): WizardActions {
 export function WizardProvider({ children }: { children: ReactNode }) {
   const [open, setOpen] = useState(false);
   // Passive observer of the account App fetches (enabled:false → reads cache, re-renders on update).
-  const { data: me } = useQuery({ queryKey: ["me"], queryFn: api.me, enabled: false });
+  const { data: me } = useQuery({ queryKey: qk.me(), queryFn: api.me, enabled: false });
 
   const openWizard = useCallback(() => setOpen(true), []);
   const closeWizard = useCallback(() => setOpen(false), []);