refactor(wizard): move onboarding wizard state into WizardProvider

Lift the onboarding wizard's open state, first-login auto-open effect, and the
wizard render itself out of App into WizardProvider. Feed, Channels, and
SettingsPanel trigger it via useWizard() instead of an onOpenWizard prop; App
and ChannelPage drop the prop plumbing. First step of S6b.3 — removing the
per-module props that block a uniform registry render. (Platform S6b.3)

frontend/src/components/Feed.tsx

@@ -32,6 +32,7 @@ import { FEED_VIEWS, type FeedView } from "../lib/feedView";
 import { clearedFilters, useActiveFilters } from "../lib/useActiveFilters";
 import ActiveFilterChips from "./ActiveFilterChips";
 import { PageToolbar } from "./PageShell";
+import { useWizard } from "./WizardProvider";
 import ViewSwitcher from "./ViewSwitcher";
 import VirtualFeed from "./VirtualFeed";
 // Lazy: the in-app YouTube player (IFrame API) loads only when a video is first opened.
@@ -85,7 +86,6 @@ export default function Feed({
   setView,
   canRead,
   isDemo = false,
-  onOpenWizard,
   ytSearch,
   onYtSearch,
   onExitYtSearch,
@@ -93,13 +93,13 @@ export default function Feed({
 }: {
   filters: FeedFilters;
   setFilters: (f: FeedFilters) => void;
-  // The view mode is an account pref, not a filter: App owns it and it persists on pick, so it
-  // isn't part of FeedFilters (no share-link param, no saved view, no active-filter chip).
+  // The view mode is an account pref, not a filter: it persists on pick, so it isn't part of
+  // FeedFilters (no share-link param, no saved view, no active-filter chip). Provided by the caller
+  // (FeedViewProvider on the feed page; ChannelPage threads its own).
   view: FeedView;
   setView: (v: FeedView) => void;
   canRead: boolean;
   isDemo?: boolean;
-  onOpenWizard: () => void;
   // Live YouTube search: the active search term (null = normal feed). Entering a search and
   // leaving it both step browser history (the search is a feed sub-view with its own history
   // entry), so the empty-state CTA enters via onYtSearch and "back to feed" pops via
@@ -112,6 +112,8 @@ export default function Feed({
   channelScoped?: boolean;
 }) {
   const { t } = useTranslation();
+  // "Connect YouTube" onboarding lives in WizardProvider (the empty-state CTA when not connected).
+  const { openWizard: onOpenWizard } = useWizard();
   // Same list the panel's badge counts — see lib/useActiveFilters.
   const activeFilters = useActiveFilters(filters, setFilters);
   const sortKeys = channelScoped