feat: add core PWA screens (auth, dashboard, purchases, products, alerts, settings)

Build all 8 primary screens for CAR-33 on top of the Phase 1 scaffold:
- Auth: login, register, forgot password with JWT flow and mock fallback
- Dashboard: triggered alerts banner, spending stats, price trend sparklines (Recharts), recent purchases
- Purchase History: store filter chips, paginated list with item previews
- Purchase Detail: receipt view with line items linking to product pages
- Products: search with instant filter, store price comparison badges
- Product Detail: 90-day price history chart (Recharts), store comparison table
- Store Comparison: ranked store cards with savings banner
- Price Alerts: triggered/watching sections, create form, progress bars, delete
- Coupons: expiration warnings, copy-to-clipboard coupon codes
- Account Linking: connect Meijer/Kroger/Target with status indicators
- Settings: profile, connected stores, notification toggles, theme switcher, sign out

Also adds:
- Mock data layer (src/lib/mock-data.ts) for demo/screenshot use
- StoreIcon component with store brand colors
- Code-split Recharts chunk (initial JS: 117KB, Recharts lazy: 498KB)
- All 48px+ touch targets, mobile-first Tailwind layout

Co-Authored-By: Paperclip <noreply@paperclip.ing>

src/App.tsx

@@ -0,0 +1,51 @@
+import { BrowserRouter, Routes, Route } from 'react-router-dom'
+import { QueryClient, QueryClientProvider } from '@tanstack/react-query'
+import { Layout } from './components/Layout.tsx'
+import { Dashboard } from './pages/Dashboard.tsx'
+import { Purchases } from './pages/Purchases.tsx'
+import { PurchaseDetail } from './pages/PurchaseDetail.tsx'
+import { Products } from './pages/Products.tsx'
+import { ProductDetail } from './pages/ProductDetail.tsx'
+import { StoreComparison } from './pages/StoreComparison.tsx'
+import { Coupons } from './pages/Coupons.tsx'
+import { Alerts } from './pages/Alerts.tsx'
+import { Settings } from './pages/Settings.tsx'
+import { AccountLinking } from './pages/AccountLinking.tsx'
+import { Login } from './pages/Login.tsx'
+import { Register } from './pages/Register.tsx'
+import { ForgotPassword } from './pages/ForgotPassword.tsx'
+
+const queryClient = new QueryClient({
+  defaultOptions: {
+    queries: {
+      staleTime: 1000 * 60 * 5,
+      retry: 1,
+    },
+  },
+})
+
+export default function App() {
+  return (
+    <QueryClientProvider client={queryClient}>
+      <BrowserRouter>
+        <Routes>
+          <Route element={<Layout />}>
+            <Route index element={<Dashboard />} />
+            <Route path="purchases" element={<Purchases />} />
+            <Route path="purchases/:id" element={<PurchaseDetail />} />
+            <Route path="products" element={<Products />} />
+            <Route path="products/:id" element={<ProductDetail />} />
+            <Route path="compare/:productId" element={<StoreComparison />} />
+            <Route path="coupons" element={<Coupons />} />
+            <Route path="alerts" element={<Alerts />} />
+            <Route path="settings" element={<Settings />} />
+            <Route path="account-linking" element={<AccountLinking />} />
+          </Route>
+          <Route path="login" element={<Login />} />
+          <Route path="register" element={<Register />} />
+          <Route path="forgot-password" element={<ForgotPassword />} />
+        </Routes>
+      </BrowserRouter>
+    </QueryClientProvider>
+  )
+}