feat(nodes): remote ingress via Traefik file provider

Remote replicas publish an ephemeral host port; the agent reports the
assigned binding back in the create_container result and the backend
renders a per-service file-provider config into TRAEFIK_DYNAMIC_DIR
pointing Traefik at the node's mesh IP + port. Routes are rewritten on
every remote reconcile and removed on teardown or local placement.

Also: RetireService retires remote leftovers when a service returns to
local placement; remove_container is idempotent agent-side; tombstoned
replicas skip remove dispatch; the domains-stay-local ceiling is gone.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

app/backend/internal/deployment/runtime.go

@@ -182,6 +182,12 @@ func (de *DeploymentEngine) ReconcileService(ctx context.Context, spec RuntimeSp
 		}
 		return de.nodeRunner.ReconcileAuto(ctx, spec)
 	}
+	// Local placement: retire any remote leftovers from a previous pin,
+	// spread, or tag affinity before reconciling local replicas.
+	if de.nodeRunner != nil {
+		_ = de.nodeRunner.RetireService(ctx, spec.ServiceID)
+	}
+
 	if spec.Replicas < 1 {
 		spec.Replicas = 1
 	}