Revert to local timezone display for user-facing times

- Changed formatTime back to use toLocaleTimeString (local time)
- Changed formatDateTime back to use toLocaleString (local time)
- App now displays all times in user's local timezone
- Backend still stores times in UTC, frontend converts for display

Makefile

@@ -48,14 +48,20 @@ dev:
 	cd frontend && npm run dev & \
 	wait
 
+# TEST variable can be used to select specific tests:
+# Backend: TEST="-m auth" (marker) or TEST="tests/test_booking.py" (file) or TEST="tests/test_booking.py::TestBooking::test_specific" (specific test)
+# Frontend: TEST="app/login" (file pattern matching app/**/*.test.{ts,tsx})
+# E2E: TEST="auth" (file pattern matching e2e/*.spec.ts)
+TEST ?=
+
 test-backend: db-clean db-ready
-	cd backend && uv run pytest -v
+	cd backend && uv run pytest -v $(TEST)
 
 test-frontend:
-	cd frontend && npm run test
+	cd frontend && npm run test $(if $(TEST),-- $(TEST),)
 
 test-e2e: db-clean db-ready
-	./scripts/e2e.sh
+	./scripts/e2e.sh $(TEST)
 
 test: check-constants check-types-fresh test-backend test-frontend test-e2e