refactor: component files export only components; lint fails on a warning

The 43 react-refresh/only-export-components warnings the gate let through meant an edit to a
provider (or AnchoredPopover, Toaster, plexDetailUi, …) could not be hot-swapped: Fast Refresh
reloads a module that also exports hooks or helpers.

- Each provider's contexts, the types its hooks return and the hooks themselves live in a sibling
  context module (navigationContext.ts, channelsContext.ts, …); the provider file keeps the
  component. loadAccountFilters moved next to the feed filters' defaults (feedFiltersInit.ts),
  following navigationInit/playlistsInit.
- Helpers that sat in component files have their own modules: welcomeMode, downloadTitle,
  plexPlayable, channelSync, ui/anchoredPopoverHooks, ui/pageToolbarSlot, ui/pagerContent,
  ui/toastLevels, ui/overlayOrder, ui/tableAlign, lib/plexDetail; the cells of the channel columns
  and the registry's page wrappers are components files of their own (channelCells, modulePages).
- usePersistedTab, an alias of useAccountPersistedState, is gone; its callers use the original.

npm run lint is now eslint --max-warnings 0, so a warning fails the gate like an error does.

frontend/src/components/WizardProvider.tsx

@@ -1,18 +1,9 @@
-import {
-  createContext,
-  lazy,
-  Suspense,
-  useCallback,
-  useContext,
-  useEffect,
-  useMemo,
-  useState,
-  type ReactNode,
-} from "react";
+import { lazy, Suspense, useCallback, useEffect, useMemo, 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";
+import { WizardActionsContext, type WizardActions } from "./wizardContext";
 
 const OnboardingWizard = lazy(() => import("./OnboardingWizard"));
 
@@ -24,22 +15,8 @@ const OnboardingWizard = lazy(() => import("./OnboardingWizard"));
 // 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 qk.me() observer (BootGate owns
 // the fetching query), so it re-runs the auto-open check when the account's grants change.
-
-interface WizardActions {
-  openWizard: () => void;
-  closeWizard: () => void;
-}
-
-// Only the actions are shared — the open flag stays local to the provider (it renders the wizard
-// itself), so no consumer needs to subscribe to it.
-const ActionsContext = createContext<WizardActions>({
-  openWizard: () => {},
-  closeWizard: () => {},
-});
-
-export function useWizard(): WizardActions {
-  return useContext(ActionsContext);
-}
+//
+// The actions context + hook live in wizardContext.ts.
 
 export function WizardProvider({ children }: { children: ReactNode }) {
   const [open, setOpen] = useState(false);
@@ -71,13 +48,13 @@ export function WizardProvider({ children }: { children: ReactNode }) {
   );
 
   return (
-    <ActionsContext.Provider value={actions}>
+    <WizardActionsContext.Provider value={actions}>
       {children}
       {/* The wizard is a full-screen overlay; the demo account can't connect YouTube, so it never
           opens there. Lazy — its chunk loads only when first opened. */}
       <Suspense fallback={null}>
         {open && me && !me.is_demo && <OnboardingWizard me={me} onClose={closeWizard} />}
       </Suspense>
-    </ActionsContext.Provider>
+    </WizardActionsContext.Provider>
   );
 }