refactor(nav): read navigation from context, drop the prop-drilling

VideoCard/PlayerModal read openChannel from useNavigationActions (the memo'd
VideoCard subscribes to the STABLE actions context, so a page/channel change
no longer re-renders it); NavSidebar/Header read page/setPage; ChannelPage
reads closeChannel; NotificationsPanel reads setPage. App sheds the matching
props, and Feed/VirtualFeed no longer thread onOpenChannel at all.

frontend/src/App.tsx

@@ -148,7 +148,7 @@ function loadInitialFilters(): FeedFilters {
 export default function App() {
   const { t, i18n } = useTranslation();
   const { page, channelView, ytSearch } = useNavigation();
-  const { setPage, openChannel, closeChannel, enterYtSearch, exitYtSearch } = useNavigationActions();
+  const { setPage, openChannel, enterYtSearch, exitYtSearch } = useNavigationActions();
   const [theme, setThemeState] = useState<ThemePrefs>(() => loadLocalTheme());
   const [filters, setFiltersState] = useState<FeedFilters>(loadInitialFilters);
   // Whether this load arrived via a "Share view" link (captured once, before the URL is stripped)
@@ -636,8 +636,6 @@ export default function App() {
     <div className="h-screen flex text-fg">
       <NavSidebar
         me={meQuery.data!}
-        page={page}
-        setPage={setPage}
         onOpenAbout={() => setAboutOpen(true)}
         onChangeLanguage={changeLanguage}
         language={i18n.language as LangCode}
@@ -699,8 +697,6 @@ export default function App() {
               me={meQuery.data!}
               view={view}
               setView={setView}
-              onBack={closeChannel}
-              onOpenChannel={openChannel}
               onShowInFeed={() => {
                 // Keep the rest of the feed's filters — the point is "this channel, the way I
                 // normally read": unwatched, my tags, my date window.
@@ -730,8 +726,6 @@ export default function App() {
           setChannelsSearch={setChannelsSearch}
           playlistsSearch={playlistsSearch}
           setPlaylistsSearch={setPlaylistsSearch}
-          page={page}
-          setPage={setPage}
           onYtSearch={enterYtSearch}
           onGoToFullHistory={() => {
             setChannelFilter("needs_full");
@@ -789,7 +783,7 @@ export default function App() {
               setSelectedId={setSelectedPlaylistId}
             />
           ) : page === "notifications" ? (
-            <NotificationsPanel filters={filters} setFilters={setFilters} setPage={setPage} onFocusChannel={focusChannel} />
+            <NotificationsPanel filters={filters} setFilters={setFilters} onFocusChannel={focusChannel} />
           ) : page === "messages" && !meQuery.data!.is_demo ? (
             <div className="p-4 max-w-3xl w-full mx-auto">
               <Messages meId={meQuery.data!.id} />
@@ -826,7 +820,6 @@ export default function App() {
               ytSearch={ytSearch}
               onYtSearch={enterYtSearch}
               onExitYtSearch={exitYtSearch}
-              onOpenChannel={openChannel}
             />
           )}
           </Suspense>