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>

README.md

@@ -85,9 +85,22 @@ PORT=3000
 ### Running Tests
 
 ```bash
+# Unit tests (vitest)
 pnpm test
+
+# E2E tests (Playwright) — requires the full Docker Compose stack to be running
+docker compose up -d --wait
+pnpm --filter @groombook/e2e test
+
+# Open the Playwright UI (interactive test runner)
+pnpm --filter @groombook/e2e test:ui
+
+# View the last E2E test report
+pnpm --filter @groombook/e2e test:report
 ```
 
+E2E tests target the Docker Compose stack (`http://localhost:8080`). They use API route mocking where needed so happy-path tests are deterministic without requiring seed data.
+
 ### Building
 
 ```bash