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-28-screenshots-note.txt

@@ -0,0 +1,39 @@
+Task 28: E2E Test Screenshots
+==============================
+
+EXPECTED SCREENSHOTS (generated when tests run):
+-------------------------------------------------
+
+1. .sisyphus/evidence/task-28-shift-signup.png
+   - Shows shift detail page after manager signs up
+   - Capacity: "1/3 spots filled"
+   - "Cancel Sign-up" button visible
+   - Sign-up list shows 1 member
+   
+2. .sisyphus/evidence/task-28-full-capacity.png
+   - Shows shift detail page at full capacity
+   - Capacity: "1/1 spots filled"  
+   - "Sign Up" button NOT visible (full capacity)
+   - Viewed by member1 (different user than who signed up)
+
+SCREENSHOT CONFIGURATION:
+-------------------------
+From shifts.spec.ts:
+
+  await page.screenshot({ 
+    path: '.sisyphus/evidence/task-28-shift-signup.png',
+    fullPage: true 
+  });
+
+  await page.screenshot({ 
+    path: '.sisyphus/evidence/task-28-full-capacity.png',
+    fullPage: true 
+  });
+
+These will be generated automatically when tests execute.
+
+STATUS:
+-------
+⏸️ Awaiting Docker environment to run tests and capture screenshots
+✅ Screenshot paths configured correctly in test code
+✅ Evidence directory exists and is writable