feat(04-01): wire BrowserRouter + BottomTabBar + empty Lists surface

- App.tsx: BrowserRouter with /calendar, /lists, /lists/:listId routes; / redirects to /calendar
- BottomTabBar.tsx: fixed-bottom 56px tab bar with Calendar + Lists NavLinks, active accent
- AppNav.tsx: add Calendar/Lists NavLinks to desktop sidebar (≥768px)
- ListsIndex.tsx: full-height surface with isLoading/isError/empty state branches; "+ New List" FAB placeholder
- ListDetail.tsx: placeholder stub for /lists/:listId (Plan 04-04 fills in)
- listsStore.ts: Zustand UI-only store (activeTab, createListSheetOpen)
- listsClient.ts: fetchLists + List/ListItem types (initial; Plans 04-02/03 expand)
- Fix Wave-0 RED stubs: add vitest imports so stubs execute (todo) not error on import
- Fix CalendarShell.test.tsx: wrap renderWithClient in MemoryRouter (AppNav uses NavLink)

apps/pwa/src/routes/ListDetail.test.tsx

@@ -9,6 +9,8 @@
  * Run: pnpm --filter @familysync/pwa test
  */
 
+import { describe, it } from 'vitest'
+
 describe('ListDetail — D-07 optimistic update + rollback', () => {
   it.todo('checking an item immediately updates the UI before server responds')
   it.todo('unchecking an item immediately updates the UI before server responds')