feat(01-04): create WizardContext provider and wire into App

- Create src/store/context.tsx: WizardContext, WizardProvider, useWizard hook
- useWizard throws if used outside WizardProvider (prevents silent undefined state bugs)
- Update src/App.tsx to wrap content in WizardProvider
- npm run build exits 0 with no TypeScript errors

src/App.tsx

@@ -1,7 +1,12 @@
+// src/App.tsx
+import { WizardProvider } from './store/context';
+
 export default function App() {
   return (
+    <WizardProvider>
       <div className="p-4">
         <h1 className="text-2xl font-bold">Ready2Blob</h1>
       </div>
+    </WizardProvider>
   );
 }

src/store/context.tsx

@@ -0,0 +1,29 @@
+// src/store/context.tsx
+// WizardContext, WizardProvider, and useWizard hook.
+// useWizard throws if used outside WizardProvider — prevents silent "undefined state" bugs.
+
+import React, { createContext, useContext, useReducer } from 'react';
+import { WizardState, WizardAction, INITIAL_STATE } from './types';
+import { wizardReducer } from './reducer';
+
+interface WizardContextValue {
+  state: WizardState;
+  dispatch: React.Dispatch<WizardAction>;
+}
+
+const WizardContext = createContext<WizardContextValue | null>(null);
+
+export function WizardProvider({ children }: { children: React.ReactNode }) {
+  const [state, dispatch] = useReducer(wizardReducer, INITIAL_STATE);
+  return (
+    <WizardContext.Provider value={{ state, dispatch }}>
+      {children}
+    </WizardContext.Provider>
+  );
+}
+
+export function useWizard(): WizardContextValue {
+  const ctx = useContext(WizardContext);
+  if (!ctx) throw new Error('useWizard must be used inside <WizardProvider>');
+  return ctx;
+}