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>

.github/workflows/ci.yml

@@ -48,6 +48,45 @@ jobs:
       - name: Run tests
         run: pnpm test
 
+  e2e:
+    name: E2E Tests
+    runs-on: ubuntu-latest
+    needs: [lint-typecheck, test]
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: pnpm/action-setup@v4
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 20
+          cache: pnpm
+
+      - name: Install dependencies
+        run: pnpm install --frozen-lockfile
+
+      - name: Install Playwright browsers
+        run: pnpm --filter @groombook/e2e exec playwright install --with-deps chromium
+
+      - name: Start Docker Compose stack
+        run: docker compose up -d --wait
+        timeout-minutes: 5
+
+      - name: Run E2E tests
+        run: pnpm --filter @groombook/e2e test
+
+      - name: Upload Playwright report
+        if: failure()
+        uses: actions/upload-artifact@v4
+        with:
+          name: playwright-report
+          path: apps/e2e/playwright-report/
+          retention-days: 7
+
+      - name: Stop Docker Compose stack
+        if: always()
+        run: docker compose down
+
   build:
     name: Build
     runs-on: ubuntu-latest