Add Playwright E2E testing infrastructure

- New apps/e2e workspace with @playwright/test
- playwright.config.ts targeting Docker Compose stack (http://localhost:8080)
- navigation.spec.ts: smoke tests for all pages
- book.spec.ts: full booking wizard happy-path with API mocking
- clients.spec.ts: client list and detail panel tests
- CI job: spins up docker compose, installs Playwright chromium, runs tests
- Playwright report uploaded as artifact on failure
- README docs for running E2E tests locally

Closes #40

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/e2e/package.json

@@ -0,0 +1,14 @@
+{
+  "name": "@groombook/e2e",
+  "version": "0.0.1",
+  "private": true,
+  "type": "module",
+  "scripts": {
+    "test": "playwright test",
+    "test:ui": "playwright test --ui",
+    "test:report": "playwright show-report"
+  },
+  "devDependencies": {
+    "@playwright/test": "^1.50.1"
+  }
+}