refactor(channels): scope module state in ChannelsProvider

Lift the Channels manager's shared local state (name filter, status chip,
active tab, column-reset token, focus-a-channel intent) out of App into a
split-context ChannelsProvider, nested inside NavigationProvider so its
focusChannel/goToFullHistory actions can drive navigation. The Channels page,
the header search box + sync chip, the feed filter sidebar, and the
notifications inbox all read it via useChannels()/useChannelsActions() instead
of props drilled through App. Channels also internalises onViewChannel /
onFilterByTag / onFocusChannel (nav + feed-filters straight from providers) and
takes only { me, onOpenWizard } now. App loses five useStates, the focusChannel
helper, the focus-clear effect, and a large block of per-page prop plumbing.
(Platform S6b.2)

frontend/src/components/Header.tsx

@@ -10,37 +10,34 @@ import { useNavigation, useNavigationActions } from "./NavigationProvider";
 import { useFeedFilters, useFeedFiltersActions } from "./FeedFiltersProvider";
 import { usePlaylists, usePlaylistsActions } from "./PlaylistsProvider";
 import { usePlex, usePlexActions } from "./PlexProvider";
+import { useChannels, useChannelsActions } from "./ChannelsProvider";
 
 // The floating top header: a row of glass pills over the content — a ModuleName pill (label +
 // accent dot + back/forward arrows), the module's SearchBar where it has one, and the per-user
 // sync chip at the right end.
 export default function Header({
   me,
-  channelsSearch,
-  setChannelsSearch,
   onYtSearch,
-  onGoToFullHistory,
 }: {
   me: Me;
-  channelsSearch: string;
-  setChannelsSearch: (q: string) => void;
   // Trigger a live YouTube search for the current term (feed only; hidden for the demo account,
   // which can't spend the shared quota).
   onYtSearch: (q: string) => void;
-  // Jump to the channel manager filtered to channels still missing full history.
-  onGoToFullHistory: () => void;
 }) {
   const { t } = useTranslation();
   const { page } = useNavigation();
   const { setPage } = useNavigationActions();
   const filters = useFeedFilters();
   const { setFilters } = useFeedFiltersActions();
-  // The playlists name filter lives in PlaylistsProvider (shared with its rail + detail pane); the
-  // Plex search term lives in PlexProvider (shared with its rail + browse grid).
+  // Each module's search term lives in its own provider (shared with that module's rail/content):
+  // playlists name filter, Plex search term, channels name filter. The channel sync chip's
+  // "go to full history" jump is a ChannelsProvider action.
   const { search: playlistsSearch } = usePlaylists();
   const { setSearch: setPlaylistsSearch } = usePlaylistsActions();
   const { q: plexQ } = usePlex();
   const { setQ: setPlexQ } = usePlexActions();
+  const { search: channelsSearch } = useChannels();
+  const { setSearch: setChannelsSearch, goToFullHistory: onGoToFullHistory } = useChannelsActions();
   // The ◀/▶ arrows step cyclically through the user's available modules (derived from `me`, so
   // it stays correct as modules are added/gated). Labels of every active module feed ModuleName's
   // dynamic width so the pill is sized to the widest reachable title in the current language.