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/changedetection/main.tf

@@ -43,7 +43,7 @@ resource "kubernetes_deployment" "changedetection" {
     }
   }
   spec {
-    replicas = 1
+    replicas = 0 # Scaled down — sockpuppetbrowser (headless Chromium sidecar) causes node OOM
     strategy {
       type = "Recreate"
     }