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/caretta.tf

@@ -14,6 +14,18 @@ resource "helm_release" "caretta" {
     victoria-metrics-single = {
       enabled = false
     }
+    tolerations = [
+      {
+        key      = "node-role.kubernetes.io/control-plane"
+        operator = "Exists"
+        effect   = "NoSchedule"
+      },
+      {
+        key      = "nvidia.com/gpu"
+        operator = "Exists"
+        effect   = "NoSchedule"
+      }
+    ]
     resources = {
       requests = {
         cpu    = "10m"