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/WizardProvider.tsx

@@ -0,0 +1,66 @@
+import {
+  createContext,
+  lazy,
+  Suspense,
+  useCallback,
+  useContext,
+  useEffect,
+  useMemo,
+  useState,
+  type ReactNode,
+} from "react";
+import { useQuery } from "@tanstack/react-query";
+import { api } from "../lib/api";
+import { shouldAutoOpenOnboarding } from "../lib/onboarding";
+
+const OnboardingWizard = lazy(() => import("./OnboardingWizard"));
+
+// Owns the onboarding wizard's open state (and the wizard render itself), lifted out of App so any
+// module can trigger "connect YouTube" via a hook instead of an onOpenWizard prop threaded through
+// the tree. Mirrors the other split-context providers; composed in main.tsx around <App/>.
+//
+// The wizard auto-opens on first login for accounts that still need to connect YouTube (derived from
+// granted scopes + storage flags, so it's stable across the OAuth round-trip) and is reopenable from
+// Settings / the notify "reconnect" action. It reads `me` as a passive ["me"] observer (App owns the
+// fetching query), so it re-runs the auto-open check when the account resolves or its grants change.
+
+interface WizardActions {
+  openWizard: () => void;
+  closeWizard: () => void;
+}
+
+// Only the actions are shared — the open flag stays local to the provider (it renders the wizard
+// itself), so no consumer needs to subscribe to it.
+const ActionsContext = createContext<WizardActions>({ openWizard: () => {}, closeWizard: () => {} });
+
+export function useWizard(): WizardActions {
+  return useContext(ActionsContext);
+}
+
+export function WizardProvider({ children }: { children: ReactNode }) {
+  const [open, setOpen] = useState(false);
+  // Passive observer of the account App fetches (enabled:false → reads cache, re-renders on update).
+  const { data: me } = useQuery({ queryKey: ["me"], queryFn: api.me, enabled: false });
+
+  const openWizard = useCallback(() => setOpen(true), []);
+  const closeWizard = useCallback(() => setOpen(false), []);
+
+  // First-login onboarding: prompt the user to connect YouTube (and resume the flow after each
+  // consent redirect). Re-checked when the account or its grants change.
+  useEffect(() => {
+    if (me && shouldAutoOpenOnboarding(me)) setOpen(true);
+  }, [me?.id, me?.can_read, me?.can_write]);
+
+  const actions = useMemo<WizardActions>(() => ({ openWizard, closeWizard }), [openWizard, closeWizard]);
+
+  return (
+    <ActionsContext.Provider value={actions}>
+      {children}
+      {/* The wizard is a full-screen overlay; the demo account can't connect YouTube, so it never
+          opens there. Lazy — its chunk loads only when first opened. */}
+      <Suspense fallback={null}>
+        {open && me && !me.is_demo && <OnboardingWizard me={me} onClose={closeWizard} />}
+      </Suspense>
+    </ActionsContext.Provider>
+  );
+}