Repomix server monitoring

Cloud Monitoring dashboard definition for repomix-server-us.

Log-based metrics used by the dashboard are managed directly in the GCP Console (logging.googleapis.com/user/oom_terminations and container_killed). They persist on the project and do not need to be redefined here.

Apply the dashboard

# Create
gcloud monitoring dashboards create --config-from-file=dashboard.json --project=repomix

# Update (use the dashboard ID from `gcloud monitoring dashboards list`)
gcloud monitoring dashboards update projects/repomix/dashboards/ \\
  --config-from-file=dashboard.json --project=repomix