Document the per-target egressProxy.hostNetwork YAML option and the
real-deps-500m production-ready throughput acceptance profile in
docs/reference/platform-infra.md, and add a single-active guard to the
k3s-build-benchmark start path so a new run deletes any prior target+profile
Job before applying the new one (preventing concurrent runs from making
status report the wrong Job, observed during #1077 regression on D518).
Basis: merges PR #1065 (real k3s dependency proxy benchmark + hostNetwork
egress proxy) as the production-ready scaffold; validated on D601 and D518
with real-deps-500m (both succeeded, apk=1231/npm=850/go=693/real_deps=2774
MiB, proxyserver cumulative 2.4 GiB / 10 GiB).
Codex