feat: embed k3s in neuron-web image to run soul-demo as managed pods

soul-demo now runs as a k3s Deployment with HPA (1–8 replicas, 60% CPU
target) instead of a bare background process. k3s starts first in
entrypoint.sh, imports the soul-demo:local OCI tar from
/var/lib/rancher/k3s/agent/images, and auto-applies the Deployment,
NodePort Service, and HPA from the server/manifests dir. neuron-web
starts only after the soul-demo pod is Running. Cloud Run gen2 execution
environment required for k3s (provides /dev/kmsg and Linux capabilities).

dist/k3s-soul-demo.yaml

@@ -0,0 +1,90 @@
+---
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: soul-demo
+  namespace: default
+  labels:
+    app: soul-demo
+spec:
+  replicas: 1
+  selector:
+    matchLabels:
+      app: soul-demo
+  template:
+    metadata:
+      labels:
+        app: soul-demo
+    spec:
+      containers:
+      - name: soul-demo
+        image: soul-demo:local
+        imagePullPolicy: Never
+        ports:
+        - containerPort: 7772
+        env:
+        - name: NEURON_HOME
+          value: /srv/soul/engram-demo
+        - name: NEURON_PORT
+          value: "7772"
+        resources:
+          requests:
+            cpu: 250m
+            memory: 256Mi
+          limits:
+            cpu: 1000m
+            memory: 512Mi
+        livenessProbe:
+          httpGet:
+            path: /healthz
+            port: 7772
+          initialDelaySeconds: 10
+          periodSeconds: 15
+          failureThreshold: 3
+        readinessProbe:
+          httpGet:
+            path: /healthz
+            port: 7772
+          initialDelaySeconds: 5
+          periodSeconds: 10
+        volumeMounts:
+        - name: engram-data
+          mountPath: /srv/soul/engram-demo
+      volumes:
+      - name: engram-data
+        emptyDir: {}
+---
+apiVersion: v1
+kind: Service
+metadata:
+  name: soul-demo
+  namespace: default
+spec:
+  type: NodePort
+  selector:
+    app: soul-demo
+  ports:
+  - port: 7772
+    targetPort: 7772
+    nodePort: 7772
+    protocol: TCP
+---
+apiVersion: autoscaling/v2
+kind: HorizontalPodAutoscaler
+metadata:
+  name: soul-demo
+  namespace: default
+spec:
+  scaleTargetRef:
+    apiVersion: apps/v1
+    kind: Deployment
+    name: soul-demo
+  minReplicas: 1
+  maxReplicas: 8
+  metrics:
+  - type: Resource
+    resource:
+      name: cpu
+      target:
+        type: Utilization
+        averageUtilization: 60