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/vitest.config.ts

@@ -0,0 +1,21 @@
+import { defineConfig } from 'vitest/config';
+
+export default defineConfig({
+  test: {
+    name: '@ketopath/shared',
+    environment: 'node',
+    include: ['src/**/*.test.ts'],
+    coverage: {
+      provider: 'v8',
+      reporter: ['text', 'html'],
+      include: ['src/**/*.ts'],
+      exclude: ['src/**/*.test.ts', 'src/index.ts'],
+      thresholds: {
+        statements: 70,
+        branches: 70,
+        functions: 70,
+        lines: 70,
+      },
+    },
+  },
+});