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/lib/queryKeys.ts

@@ -41,4 +41,62 @@ export const qk = {
     id !== undefined ? (["playlist", id] as const) : (["playlist"] as const),
   playlistMembership: (videoId: string) => ["playlist-membership", videoId] as const,
   savedViews: () => ["saved-views"] as const,
+
+  // --- account / misc (R7 S2b) --- (me/myStatus/tags already declared as shared roots above)
+  accounts: () => ["accounts"] as const,
+  version: () => ["version"] as const,
+  setupStatus: () => ["setup-status"] as const,
+  myUsage: () => ["my-usage"] as const,
+  scheduler: () => ["scheduler"] as const,
+
+  // --- notifications ---
+  notifications: () => ["notifications"] as const,
+  notifUnread: () => ["notif-unread"] as const,
+
+  // --- messaging ---
+  conversations: () => ["conversations"] as const,
+  thread: (partnerId: number | null) => ["thread", partnerId] as const,
+  messageKey: () => ["message-key"] as const,
+  messageUnread: () => ["message-unread"] as const,
+  messageUsers: () => ["message-users"] as const,
+  shareRecipients: () => ["share-recipients"] as const,
+
+  // --- downloads ---
+  downloads: () => ["downloads"] as const,
+  downloadsShared: () => ["downloads-shared"] as const,
+  downloadIndex: () => ["download-index"] as const,
+  downloadUsage: () => ["download-usage"] as const,
+  downloadProfiles: () => ["download-profiles"] as const,
+  downloadLinks: (jobId: number) => ["download-links", jobId] as const,
+  dlQuota: (userId: number) => ["dl-quota", userId] as const,
+  storyboard: (jobId: number) => ["storyboard", jobId] as const,
+
+  // --- admin ---
+  adminUsers: () => ["admin-users"] as const,
+  adminInvites: () => ["admin-invites"] as const,
+  adminConfig: () => ["admin-config"] as const,
+  adminAudit: () => ["admin-audit"] as const,
+  adminStorage: () => ["admin-storage"] as const,
+  adminDownloads: () => ["admin-downloads"] as const,
+  adminQuota: (days: number) => ["admin-quota", days] as const,
+  demoWhitelist: () => ["demo-whitelist"] as const,
+
+  // --- plex ---
+  // The composite plex keys carry a heterogeneous arg list (a filters object, a ratingKeys
+  // array, a "union"/"group"/"contains" discriminator), so they take a variadic pass-through:
+  // the value this factory centralizes is the ROOT string, and TanStack keys are `unknown[]`
+  // anyway. Single-id plex keys stay precisely typed.
+  plex: () => ["plex"] as const,
+  plexWatchLink: () => ["plex-watch-link"] as const,
+  plexLibrary: (...rest: unknown[]) => ["plex-library", ...rest],
+  plexShow: (showId?: string) =>
+    showId !== undefined ? (["plex-show", showId] as const) : (["plex-show"] as const),
+  plexItem: (id: string) => ["plex-item", id] as const,
+  plexPlaylists: (...rest: unknown[]) => ["plex-playlists", ...rest],
+  plexPlaylist: (playlistId: number) => ["plex-playlist", playlistId] as const,
+  plexCollections: (...rest: unknown[]) => ["plex-collections", ...rest],
+  // facetKey is a filters-derived OBJECT segment (not a scalar), so this key is heterogeneous too.
+  plexFacets: (...rest: unknown[]) => ["plex-facets", ...rest],
+  plexPeopleCards: (scope: string, actors: string[]) =>
+    ["plex-people-cards", scope, actors] as const,
 };