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>

packages/shared/src/nutrition/bmr.ts

@@ -0,0 +1,27 @@
+import type { Gender } from './types.js';
+
+export interface BmrInput {
+  weightKg: number;
+  heightCm: number;
+  ageYears: number;
+  gender: Gender;
+}
+
+// Mifflin-St Jeor equation. For Gender 'OTHER' we use the average of the
+// male and female sex-specific constants (-78), as a neutral approximation.
+export function calculateBmr({ weightKg, heightCm, ageYears, gender }: BmrInput): number {
+  if (weightKg <= 0 || heightCm <= 0 || ageYears <= 0) {
+    throw new RangeError('weightKg, heightCm and ageYears must be positive');
+  }
+
+  const base = 10 * weightKg + 6.25 * heightCm - 5 * ageYears;
+
+  switch (gender) {
+    case 'MALE':
+      return base + 5;
+    case 'FEMALE':
+      return base - 161;
+    case 'OTHER':
+      return base - 78;
+  }
+}