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/components/CalendarShell.test.tsx

@@ -18,6 +18,7 @@ import React from 'react'
 import { describe, it, expect, vi, beforeEach, type Mock } from 'vitest'
 import { render, screen, waitFor } from '@testing-library/react'
 import { QueryClient, QueryClientProvider } from '@tanstack/react-query'
+import { MemoryRouter } from 'react-router'
 
 // window.matchMedia is polyfilled in src/test-setup.ts (loaded via vitest.config setupFiles)
 
@@ -128,7 +129,9 @@ function makeQueryClient() {
 function renderWithClient(ui: React.ReactElement) {
   const client = makeQueryClient()
   return render(
-    <QueryClientProvider client={client}>{ui}</QueryClientProvider>,
+    <MemoryRouter initialEntries={['/calendar']}>
+      <QueryClientProvider client={client}>{ui}</QueryClientProvider>
+    </MemoryRouter>,
   )
 }