#212 Register all example apps and create test workflows

Register all apps in engine/apps/examples/*.py: - math_utils (sum, double) - string_utils (concat, upper) - calculator (add, multiply, compute) - approval_gateway (approve_payment, approve_deployment, request_generic_approval) - notification_hub (send_slack, send_email, send_webhook, broadcast, send_alert_and_wait) Already registered: hello_world, long_runner Create 2 workflow types per app: 1. Normal worker (no timeout policy) 2. Activity worker (timeout > 30s)