Add node hang instrumentation and scale down chromium services

- Add journald collection to Alloy (loki.source.journal) for kernel OOM,
  panic, hung task, and soft lockup detection — ships system logs off-node
  so they survive hard resets
- Add 5 Loki alerting rules (KernelOOMKiller, KernelPanic, KernelHungTask,
  KernelSoftLockup, ContainerdDown) evaluating against node-journal logs
- Fix Loki ruler config: correct rules mount path (/var/loki/rules/fake),
  add alertmanager_url and enable_api
- Add Prometheus alerts: NodeMemoryPressureTrending (>85%), NodeExporterDown,
  NodeHighIOWait (>30%)
- Add caretta tolerations for control-plane and GPU nodes
- Scale down chromium-based services to 0 for cluster stability:
  f1-stream, flaresolverr, changedetection, resume/printer

stacks/platform/modules/monitoring/loki.yaml

@@ -33,7 +33,7 @@ loki:
     storage:
       type: local
       local:
-        directory: /loki/rules
+        directory: /var/loki/rules
     alertmanager_url: http://prometheus-alertmanager.monitoring.svc.cluster.local:9093
     ring:
       kvstore:
@@ -66,7 +66,7 @@ singleBinary:
     - name: wal
       mountPath: /loki-wal
     - name: rules
-      mountPath: /loki/rules/fake
+      mountPath: /var/loki/rules/fake
   resources:
     requests:
       cpu: 250m