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/Channels.tsx

@@ -33,6 +33,7 @@ import { useConfirm } from "./ConfirmProvider";
 import { useChannels, useChannelsActions } from "./ChannelsProvider";
 import { useNavigationActions } from "./NavigationProvider";
 import { useFeedFilters, useFeedFiltersActions } from "./FeedFiltersProvider";
+import { useWizard } from "./WizardProvider";
 
 export type ChannelsView = "subscribed" | "discovery" | "blocked";
 
@@ -45,9 +46,11 @@ const STATUS_FILTERS: { id: ChannelStatusFilter; labelKey: string }[] = [
   { id: "hidden", labelKey: "channels.filters.hidden" },
 ];
 
-export default function Channels({ me, onOpenWizard }: { me: Me; onOpenWizard: () => void }) {
+export default function Channels({ me }: { me: Me }) {
   const canWrite = me.can_write;
   const isAdmin = me.role === "admin";
+  // "Connect YouTube" onboarding lives in WizardProvider (a notify action / a mutation-error CTA).
+  const { openWizard: onOpenWizard } = useWizard();
   // The manager's name filter, status chip, active tab, reset token, and focus-channel intent live
   // in ChannelsProvider (shared with the header search box + the cross-module "focus this channel"
   // callers); this page is their primary editor.