test: aggiungi suite completa unit, integration ed e2e

- Unit (12+9): conversion.js (rawToCooked/cookedToRaw, edge case, inversa)
  e storage.js (save/load, round-trip, default fallback)
- Integration (17+12+14): Converter (ricerca, selezione, calcolo, swap, reset),
  MealPlanner (rendering, add/remove, generateShopping, deduplicazione),
  ShoppingList (add, toggle, remove, clearAll, contatore)
- E2E Playwright (6+6+7+10): navigation, meal-planner, converter, shopping-list
- Configurazione: vitest.config.js + playwright.config.js + tests/setup.js
- Script: test, test:coverage, test:e2e, test:e2e:ui

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

playwright.config.js

@@ -0,0 +1,19 @@
+import { defineConfig, devices } from '@playwright/test'
+
+export default defineConfig({
+  testDir: './tests/e2e',
+  use: {
+    baseURL: 'http://localhost:5173',
+    // Simula iPhone 14 Pro — dimensioni target dell'app
+    viewport: { width: 393, height: 852 },
+    locale: 'it-IT',
+  },
+  webServer: {
+    command: 'npm run dev',
+    url: 'http://localhost:5173',
+    reuseExistingServer: true,
+  },
+  projects: [
+    { name: 'mobile-chrome', use: { ...devices['Pixel 5'] } },
+  ],
+})