fix(lists): add items offline via the outbox; recognisable input field

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/lib/__tests__/offline.test.ts

@@ -47,3 +47,28 @@ describe('outbox', () => {
     expect(isCacheablePath('/api/v1/export/markdown')).toBe(false);
   });
 });
+
+describe('list items added offline', () => {
+  beforeEach(() => localStorage.clear());
+
+  it('show up as stand-ins and follow edits until they are sent', async () => {
+    const { pendingListItems, updateQueued, dropQueued, OFFLINE_ITEM_PREFIX } = await import('../offline');
+    const milk = enqueue('POST', '/api/v1/lists/lst_1/items', { content: 'Hafermilch', category: 'Kühlregal', quantity: '' });
+    const bread = enqueue('POST', '/api/v1/lists/lst_2/items', { content: 'Brot', category: '', quantity: '1' });
+    enqueue('POST', '/api/v1/inbox', { content: 'kein Listeneintrag' });
+
+    let items = pendingListItems();
+    expect(items.map((i) => [i.listId, i.content])).toEqual([
+      ['lst_1', 'Hafermilch'],
+      ['lst_2', 'Brot'],
+    ]);
+    expect(items[0].id).toBe(OFFLINE_ITEM_PREFIX + milk.id);
+
+    updateQueued(milk.id, { quantity: '2' });
+    dropQueued(bread.id);
+    items = pendingListItems();
+    expect(items).toHaveLength(1);
+    expect(items[0].quantity).toBe('2');
+    expect(getOutbox()).toHaveLength(2); // the inbox entry stays
+  });
+});