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>

tests/e2e/navigation.spec.js

@@ -0,0 +1,42 @@
+import { test, expect } from '@playwright/test'
+
+test.describe('Navigazione tra tab', () => {
+  test.beforeEach(async ({ page }) => {
+    await page.goto('/')
+  })
+
+  test('la tab Pasti è attiva al caricamento', async ({ page }) => {
+    await expect(page.locator('.nav-btn.active')).toContainText('Pasti')
+    await expect(page.locator('.page-title')).toContainText('Piano Pasti')
+  })
+
+  test('la tab Converti mostra il convertitore', async ({ page }) => {
+    await page.locator('.nav-btn', { hasText: 'Converti' }).click()
+    await expect(page.locator('.page-title')).toContainText('Convertitore')
+    await expect(page.locator('.nav-btn.active')).toContainText('Converti')
+  })
+
+  test('la tab Spesa mostra la lista della spesa', async ({ page }) => {
+    await page.locator('.nav-btn', { hasText: 'Spesa' }).click()
+    await expect(page.locator('.page-title')).toContainText('Lista della spesa')
+    await expect(page.locator('.nav-btn.active')).toContainText('Spesa')
+  })
+
+  test('si può tornare a Pasti da un\'altra tab', async ({ page }) => {
+    await page.locator('.nav-btn', { hasText: 'Converti' }).click()
+    await page.locator('.nav-btn', { hasText: 'Pasti' }).click()
+    await expect(page.locator('.page-title')).toContainText('Piano Pasti')
+  })
+
+  test('il pulsante info apre il pannello informazioni', async ({ page }) => {
+    await page.locator('.btn-info').click()
+    await expect(page.locator('.sheet')).toBeVisible()
+    await expect(page.locator('.app-name')).toContainText('BitePlan')
+  })
+
+  test('il pannello info si chiude con la X', async ({ page }) => {
+    await page.locator('.btn-info').click()
+    await page.locator('.btn-x').click()
+    await expect(page.locator('.sheet')).not.toBeVisible()
+  })
+})