k3s fails to start in Cloud Run gen2 with "unable to select an IP from
default routes" because Cloud Run's network sandbox doesn't expose a
standard default route for k3s to detect. The blocking wait on k3s
prevented neuron-web from ever binding port 8080, causing Cloud Run's
startup probe to time out and terminate the container.
Two changes:
1. Add --flannel-iface=eth0 so k3s pins to Cloud Run's eth0 rather than
walking the routing table to detect a default-route interface.
2. Start neuron-web immediately after launching k3s in background.
soul-demo becomes available asynchronously; neuron-web handles it
being temporarily unavailable gracefully.
will.anderson