feat(deploy): add worker / no-route app kind [SLIP-73]

[mitchelljphayes]

Add 'worker' app kind for non-HTTP workloads (background processors, pipelines).

• RoutingConfig fields become Option (backward compatible)
• Worker health = container_is_running(), no HTTP health check
• Docker/Podman skip port binding when container_port == 0
• All deploy paths guard route ops with if !is_worker
• PreviewState.domain becomes Option
• Kind field on AppStatusResponse, AppRuntimeState, PersistedAppState
• Kind persisted across restarts
• Unknown kinds produce validation errors
• 6 new tests (333 total)

SLIP-73