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/types/api.ts

@@ -0,0 +1,65 @@
+export interface Purchase {
+  id: string
+  storeId: string
+  storeName: string
+  date: string
+  total: number
+  items: PurchaseItem[]
+}
+
+export interface PurchaseItem {
+  id: string
+  productId: string
+  name: string
+  quantity: number
+  price: number
+  unitPrice: number
+}
+
+export interface Product {
+  id: string
+  name: string
+  brand: string
+  category: string
+  imageUrl?: string
+  prices: ProductPrice[]
+}
+
+export interface ProductPrice {
+  storeId: string
+  storeName: string
+  price: number
+  lastUpdated: string
+}
+
+export interface PriceHistory {
+  date: string
+  price: number
+  storeId: string
+}
+
+export interface Coupon {
+  id: string
+  productId?: string
+  storeName: string
+  description: string
+  discount: string
+  expiresAt: string
+  code?: string
+}
+
+export interface PriceAlert {
+  id: string
+  productId: string
+  productName: string
+  targetPrice: number
+  currentPrice: number
+  triggered: boolean
+}
+
+export interface User {
+  id: string
+  email: string
+  name: string
+  connectedStores: string[]
+}