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-26-auth-flow.txt

@@ -0,0 +1,23 @@
+PLACEHOLDER: Screenshot will be generated when tests run with full environment
+
+Expected screenshot content:
+- URL: http://localhost:3000/dashboard
+- Page title: "Welcome to Sunrise Tennis Club" (or active club name)
+- Header: ClubSwitcher button showing "Sunrise Tennis Club" with badge
+- Dashboard cards showing:
+  * My Open Tasks (count)
+  * My Upcoming Shifts (count)
+- Navigation sidebar with Dashboard, Tasks, Shifts, Members links
+- Sign Out button in header
+
+Test scenario captured:
+1. Unauthenticated user navigates to /dashboard
+2. Redirected to /login
+3. Clicks "Sign in with Keycloak"
+4. Redirected to Keycloak login page (localhost:8080)
+5. Enters credentials: admin@test.com / testpass123
+6. Submits login form
+7. Redirected back to app at /select-club
+8. Selects first club card
+9. Redirected to /dashboard
+10. Dashboard loads with club-specific data