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/hooks/useListSSE.test.ts

@@ -10,6 +10,8 @@
  * Run: pnpm --filter @familysync/pwa test
  */
 
+import { describe, it } from 'vitest'
+
 describe('useListSSE — D-11 bounded backoff', () => {
   it.todo('starts connected when EventSource fires the open event')
   it.todo('attempts to reconnect with exponential backoff on error')