feat(01-04): wire Items components in App

- Import ItemForm and ItemsList
- Add Items section after People section
- App now supports full bill entry workflow

gsd-framework/src/app.jsx

@@ -1,5 +1,7 @@
 import { PersonForm } from './components/people/PersonForm.jsx';
 import { PeopleList } from './components/people/PeopleList.jsx';
+import { ItemForm } from './components/items/ItemForm.jsx';
+import { ItemsList } from './components/items/ItemsList.jsx';
 
 export function App() {
   return (
@@ -11,6 +13,12 @@ export function App() {
         <PersonForm />
         <PeopleList />
       </section>
+
+      <section class="items-section">
+        <h2>Items</h2>
+        <ItemForm />
+        <ItemsList />
+      </section>
     </div>
   );
 }