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/moduleRegistry.tsx

@@ -2,14 +2,9 @@ import type { ComponentType } from "react";
 import { lazyWithPreload, type PreloadableComponent } from "../lib/lazyWithPreload";
 import type { Page } from "../lib/urlState";
 import type { PanelId, PanelLayout } from "../lib/panelLayout";
-import { useMe } from "../lib/useMe";
-import { useFeedFilters, useFeedFiltersActions } from "./FeedFiltersProvider";
-import { useFeedView, useFeedViewActions } from "./FeedViewProvider";
-import { useNavigation, useNavigationActions } from "./NavigationProvider";
 import Sidebar from "./Sidebar";
 import PlaylistsRail from "./PlaylistsRail";
-import PersonalViewsModal from "./PersonalViewsModal";
-import { useSavedViews } from "./SavedViewsProvider";
+import { Feed, FeedPage, Messages, MessagesPage } from "./modulePages";
 
 // The RENDER half of the module registry: which component (and side rail) each page renders. The
 // metadata half — nav order, label, icon, gate — lives in lib/modules.ts (imported by NavSidebar /
@@ -18,21 +13,19 @@ import { useSavedViews } from "./SavedViewsProvider";
 //
 // Every content entry is a PROP-FREE component: it reads `me` from useMe() and its module-local state
 // from the scoped providers, so App renders `<Content />` uniformly. The two that need per-render
-// wiring get a thin wrapper here (FeedPage supplies the GLOBAL feed scope; the channel page threads
-// its own isolated scope to <Feed> directly — see the scope note in FeedFiltersProvider).
+// wiring get a thin wrapper in modulePages (FeedPage supplies the GLOBAL feed scope; the channel page
+// threads its own isolated scope to <Feed> directly — see the scope note in FeedFiltersProvider).
 
 // Route-level code splitting: each page is its own lazy chunk (admin-only pages never reach
 // non-admins; the logged-out landing pulls only the shell). Rendered inside App's <Suspense>. Each
 // one is preloadable: App fetches the chunks of every page the account can reach once the first page
 // is on screen (preloadPages below), so switching modules never shows the chunk fallback.
 const Home = lazyWithPreload(() => import("./Home"));
-const Feed = lazyWithPreload(() => import("./Feed"));
 const Channels = lazyWithPreload(() => import("./Channels"));
 const Playlists = lazyWithPreload(() => import("./Playlists"));
 const PlexBrowse = lazyWithPreload(() => import("./PlexBrowse"));
 const PlexSidebar = lazyWithPreload(() => import("./PlexSidebar"));
 const NotificationsPanel = lazyWithPreload(() => import("./NotificationsPanel"));
-const Messages = lazyWithPreload(() => import("./Messages"));
 const DownloadCenter = lazyWithPreload(() => import("./DownloadCenter"));
 const Stats = lazyWithPreload(() => import("./Stats"));
 const Scheduler = lazyWithPreload(() => import("./Scheduler"));
@@ -41,47 +34,6 @@ const AdminUsers = lazyWithPreload(() => import("./AdminUsers"));
 const AuditLog = lazyWithPreload(() => import("./AuditLog"));
 const SettingsPanel = lazyWithPreload(() => import("./SettingsPanel"));
 
-// The GLOBAL feed page: wires <Feed> to the app-wide feed filters / view / live-search. (The channel
-// page renders <Feed> itself with its own channel-scoped filters, so those two never share state.)
-function FeedPage() {
-  const me = useMe();
-  const filters = useFeedFilters();
-  const { setFilters } = useFeedFiltersActions();
-  const view = useFeedView();
-  const { setView } = useFeedViewActions();
-  const { ytSearch } = useNavigation();
-  const { enterYtSearch, exitYtSearch } = useNavigationActions();
-  // The Personal Views modal lives at the feed-page level (always mounted while on the feed, unmounts
-  // on navigation) rather than inside the collapsible filter rail — otherwise opening it from the
-  // always-visible toolbar view chip while the rail is unpinned would render nothing and latch open.
-  const { modalOpen } = useSavedViews();
-  return (
-    <>
-      <Feed
-        filters={filters}
-        setFilters={setFilters}
-        view={view}
-        setView={setView}
-        canRead={me.can_read}
-        isDemo={me.is_demo}
-        ytSearch={ytSearch}
-        onYtSearch={enterYtSearch}
-        onExitYtSearch={exitYtSearch}
-      />
-      {modalOpen && !me.is_demo && <PersonalViewsModal />}
-    </>
-  );
-}
-
-function MessagesPage() {
-  const me = useMe();
-  return (
-    <div className="p-4 max-w-3xl w-full mx-auto">
-      <Messages meId={me.id} />
-    </div>
-  );
-}
-
 export type PageDef = {
   // Prop-free by construction: reads `me` + module state from hooks/providers. Preloadable by type, so
   // a new page cannot silently opt out of preloadPages.