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-club-switch.txt

@@ -0,0 +1,19 @@
+PLACEHOLDER: Screenshot will be generated when tests run with full environment
+
+Expected screenshot content:
+- URL: http://localhost:3000/tasks
+- Page title: "Tasks"
+- Header: ClubSwitcher button showing "Valley Cycling Club" (second club)
+- Task table with club-2 specific tasks
+- Table columns: Title, Status, Assignee, Created, Actions
+- Pagination controls at bottom (if >20 tasks)
+
+Test scenario captured:
+1. User authenticated and viewing tasks for first club
+2. User clicks ClubSwitcher dropdown in header
+3. Dropdown opens showing all available clubs
+4. User clicks second club "Valley Cycling Club"
+5. TanStack Query invalidates all queries
+6. Page refreshes with new club context
+7. Tasks table updates with club-2 data
+8. Header ClubSwitcher now shows "Valley Cycling Club"