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/App.tsx

@@ -1,5 +1,38 @@
+/**
+ * App — BrowserRouter shell with react-router declarative routing.
+ *
+ * Routes:
+ *   /             → redirect to /calendar
+ *   /calendar     → CalendarShell
+ *   /lists        → ListsIndex
+ *   /lists/:listId → ListDetail (placeholder for Plan 04-04)
+ *
+ * BottomTabBar is rendered as a sibling of <Routes> so it persists across route
+ * changes. On desktop (≥768px) AppNav sidebar handles navigation — BottomTabBar
+ * is only visible on phone via CSS, but we render it in the tree at all sizes so
+ * the tab state remains consistent.
+ *
+ * navigateFallback ('/index.html') in vite.config.ts covers SPA deep-links to
+ * /lists/* — the SW denylist only excludes /callback, /api/, and /health, so
+ * /lists/* is served from cache correctly.
+ */
+
+import { BrowserRouter, Routes, Route, Navigate } from 'react-router'
 import { CalendarShell } from './components/CalendarShell.js'
+import { ListsIndex } from './routes/ListsIndex.js'
+import { ListDetail } from './routes/ListDetail.js'
+import { BottomTabBar } from './components/BottomTabBar.js'
 
 export default function App() {
-  return <CalendarShell />
+  return (
+    <BrowserRouter>
+      <Routes>
+        <Route path="/" element={<Navigate to="/calendar" replace />} />
+        <Route path="/calendar" element={<CalendarShell />} />
+        <Route path="/lists" element={<ListsIndex />} />
+        <Route path="/lists/:listId" element={<ListDetail />} />
+      </Routes>
+      <BottomTabBar />
+    </BrowserRouter>
+  )
 }