test: setup Vitest workspace and Playwright with first nutrition tests

Vitest:
- Workspace at root (vitest.workspace.ts) running per-package configs
- packages/shared/vitest.config.ts with v8 coverage and 70% thresholds
- Root scripts: test / test:watch / test:coverage

Nutrition module in @ketopath/shared:
- calculateBmr (Mifflin-St Jeor) + calculateTdee with activity multipliers
- ACTIVITY_MULTIPLIERS constants matching CLAUDE.md domain knowledge
- 14 unit tests covering Michele/Laura PRD personas, all sex variants,
  every activity level, and input validation (100% coverage on src/nutrition)

Playwright in apps/web:
- chromium-only project, webServer auto-boot of pnpm dev
- e2e/home.spec.ts smoke test asserts Italian copy and disclaimer

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/web/playwright.config.ts

@@ -0,0 +1,24 @@
+import { defineConfig, devices } from '@playwright/test';
+
+const PORT = 3000;
+const baseURL = `http://localhost:${PORT}`;
+
+export default defineConfig({
+  testDir: './e2e',
+  fullyParallel: true,
+  forbidOnly: Boolean(process.env.CI),
+  retries: process.env.CI ? 2 : 0,
+  workers: process.env.CI ? 1 : undefined,
+  reporter: process.env.CI ? 'github' : 'list',
+  use: {
+    baseURL,
+    trace: 'on-first-retry',
+  },
+  projects: [{ name: 'chromium', use: { ...devices['Desktop Chrome'] } }],
+  webServer: {
+    command: 'pnpm dev',
+    url: baseURL,
+    reuseExistingServer: !process.env.CI,
+    timeout: 120_000,
+  },
+});