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>

tsconfig.app.json

@@ -0,0 +1,28 @@
+{
+  "compilerOptions": {
+    "tsBuildInfoFile": "./node_modules/.tmp/tsconfig.app.tsbuildinfo",
+    "target": "ES2023",
+    "useDefineForClassFields": true,
+    "lib": ["ES2023", "DOM", "DOM.Iterable"],
+    "module": "ESNext",
+    "types": ["vite/client", "vitest/globals"],
+    "skipLibCheck": true,
+
+    /* Bundler mode */
+    "moduleResolution": "bundler",
+    "allowImportingTsExtensions": true,
+    "verbatimModuleSyntax": true,
+    "moduleDetection": "force",
+    "noEmit": true,
+    "jsx": "react-jsx",
+
+    /* Linting */
+    "strict": true,
+    "noUnusedLocals": true,
+    "noUnusedParameters": true,
+    "erasableSyntaxOnly": true,
+    "noFallthroughCasesInSwitch": true,
+    "noUncheckedSideEffectImports": true
+  },
+  "include": ["src"]
+}