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/store/listsStore.ts

@@ -0,0 +1,36 @@
+/**
+ * Zustand UI-state store for the lists surface.
+ *
+ * Owns ONLY UI-shape state — no server data ever enters this store.
+ * Server state (lists, items) lives in TanStack Query.
+ *
+ * Convention: follows calendarStore.ts pattern — no persist middleware,
+ * no immer. State is ephemeral; lists UI state does not need persistence.
+ *
+ * State contract:
+ *   activeTab              — which bottom-tab is selected (drives tab active-state)
+ *   createListSheetOpen    — whether the "New List" sheet/dialog is open
+ */
+
+import { create } from 'zustand'
+
+// ── Types ──────────────────────────────────────────────────────────────────
+
+export interface ListsStore {
+  // UI-only state — no server data
+  activeTab: 'calendar' | 'lists'
+  createListSheetOpen: boolean
+
+  setActiveTab: (tab: 'calendar' | 'lists') => void
+  setCreateListSheetOpen: (open: boolean) => void
+}
+
+// ── Store ──────────────────────────────────────────────────────────────────
+
+export const useListsStore = create<ListsStore>()((set) => ({
+  activeTab: 'calendar',
+  createListSheetOpen: false,
+
+  setActiveTab: (tab) => set({ activeTab: tab }),
+  setCreateListSheetOpen: (open) => set({ createListSheetOpen: open }),
+}))