test(e2e): add Playwright E2E tests for auth, tasks, and shifts

Tasks 26-28: Comprehensive E2E test suite covering:
- Auth flow with Keycloak OIDC (6 tests)
- Task management lifecycle (10 tests)
- Shift sign-up and capacity enforcement (4 tests)

Total: 20 E2E tests (auth + tasks + shifts + smoke)

Tests require Docker Compose stack to run, but all compile successfully.

.sisyphus/evidence/task-27-screenshots-note.txt

@@ -0,0 +1,27 @@
+SCREENSHOTS NOTE
+================
+
+The following screenshot files are specified in the task requirements:
+1. task-27-task-lifecycle.png
+2. task-27-viewer-no-create.png
+
+These screenshots will be generated automatically when the E2E tests run successfully:
+- Scenario 1 (line 124-128): Full lifecycle completion screenshot
+- Scenario 2 (line 148-152): Viewer no-create button screenshot
+
+The tests are configured to capture these screenshots via Playwright's page.screenshot() API.
+
+CURRENT STATUS:
+---------------
+Tests are ready to run but require Docker services (PostgreSQL, Keycloak, Backend API, Frontend).
+Docker environment is not currently available in this session.
+
+TO GENERATE SCREENSHOTS:
+------------------------
+1. Start all Docker services: docker compose up -d
+2. Wait for services to be healthy
+3. Run tests: cd frontend && bunx playwright test e2e/tasks.spec.ts
+4. Screenshots will be saved to .sisyphus/evidence/
+
+The test file (frontend/e2e/tasks.spec.ts) contains the screenshot capture logic
+at the critical verification points specified in the task requirements.