operator: re-measure resource sizing at scale; the equations under-size large clusters #839

Problem

The operator's sizing guidance, docs/operations/resources-at-scale.md and the chart's default resource calculation from estimatedNodeCount and estimatedPackageCount (chart/templates/deployment.yaml), is validated only up to 1k nodes. It no longer describes how the operator uses memory:

• The equations take only node and package count. perf(operator): cut reconcile-path allocations on large clusters #797 profiled a cluster of about 2,700 nodes and 80,000 pods: after that change the live heap is about 2.5 GiB, and the Pod cache is the largest part of it. That cache is cluster-wide because drain has to see every pod, so pod count is a missing input.
• The equations predate package execution as Jobs. The doc already says they were not re-measured with the Jobs informer in the cache.
• At that scale perf(operator): cut reconcile-path allocations on large clusters #797 puts the realistic floor at a 6 Gi limit, or 4 Gi with GOMEMLIMIT set, because with default GOGC the heap peaks near twice live. Before perf(operator): cut reconcile-path allocations on large clusters #797 the operator crash-looped at 4 Gi and needed 12 Gi to stay up (operator: reconcile path allocates far more than it retains on large clusters #796). For the same cluster, estimatedNodeCount: 2700 with one or two packages makes the chart compute a 2160Mi limit.
• Nothing sets GOMEMLIMIT, in the chart or in operator/config.
• The chart sets the memory request to 0.4 × N; the doc says 0.45 × N.

Proposal

Redo the sizing investigation on top of #797, at several cluster sizes including at least one past 2k nodes, varying pod count and retained Jobs (jobTtlSucceeded) along with node and package count. The opt-in pprof endpoint in #795 would make the profiling repeatable. From the results:

• Update the equations and the validated range in resources-at-scale.md.
• Update the chart calculation to match. Add a pod-count input if the data shows it is needed.
• Decide whether the chart should derive GOMEMLIMIT from the memory limit.

Follows #797 and #796.