Improve English translation

[ianychoi]

The followings are the list of files which translated (into English) amount is quite different from Korean docs.

1. Very large (1,500+ lines) — recommend an umbrella issue + section splitting (6 files)

eks-pod-health-lifecycle.md (5,592 lines)
eks-resource-optimization.md (5,411 lines)
eks-pod-scheduling-availability.md (5,084 lines)
karpenter-autoscaling.md (3,197 lines)
cost-management.md (1,854 lines)
cilium-eni-gateway-api.md (1,822 lines)

2. Medium (600–1,500 lines) — doable by one person but sizable (3 files)

eks-resiliency-guide.md (1,492 lines)
east-west-traffic-best-practice.md (935 lines)
migration-execution-strategy.md (839 lines)

3. Small (under 600 lines) — good first issue candidates (4 files)

eks-control-plane-crd-scaling.md (599 lines, 38%)
evaluation-framework.md (530 lines, 32%)
eks-api-server-authn-authz.md (410 lines, 37%)
index.md (237 lines, 30%)

4. Separately: pages with no English translation at all (3 files): These have a Korean source but no English file, so they aren't in the table above:

open-weight-model-pipeline.md
vpc-cni-deep-dive.md
network-flow-monitor.md