docs(skills): rewrite container-security descriptions to a uniform standard

All 33 container-security skills now carry what it does, an explicit
"Use when" trigger, keywords, and a negative trigger naming the nearest
neighbour. Six collision clusters resolved by differentiating scope
rather than merging, so no skill is removed:

- kube-bench: running the tool vs interpreting findings into an audit
- Calico: portable upstream NetworkPolicy vs Calico-as-CNI vs Calico-only
  CRDs (GlobalNetworkPolicy, HostEndpoint, DNS egress)
- Falco: deploying and operating it vs authoring escape rules
- container escape: tool-agnostic runtime signals vs Falco rule syntax vs
  static posture audit vs offensive breakout
- Trivy: all-target platform and operator vs single-image scan
- Docker: images and Dockerfiles vs daemon.json vs the CIS audit script

Also replaces the templated "When to Use" boilerplate in these files,
including bullets that only restated the skill's own name.

Worst pair (Pod Security Standards vs Pod Security Admission) drops from
0.77 cosine to below the 0.45 threshold. Repo-wide: colliding pairs
60 -> 56, skills involved 105 -> 94.

skills/performing-kubernetes-etcd-security-assessment/SKILL.md

@@ -1,10 +1,13 @@
 ---
 name: performing-kubernetes-etcd-security-assessment
-description: Assess the security posture of Kubernetes etcd clusters by evaluating
-  encryption at rest, TLS transport configuration, access controls, backup encryption,
-  and network isolation for the cluster's backing key-value store. Use when auditing
-  or hardening a Kubernetes control plane, since etcd holds Secrets, RBAC policies,
-  and ConfigMaps in plaintext by default and is a high-value target if left unassessed.
+description: >-
+  Assesses the security posture of the etcd cluster backing Kubernetes: encryption at rest,
+  TLS peer and client transport, access control, backup encryption, and network isolation. Use
+  when auditing or hardening a control plane, reviewing whether Secrets are encrypted at rest,
+  or protecting etcd backups, since etcd stores Secrets, RBAC policy, and ConfigMaps in
+  plaintext by default. Keywords: etcd, EncryptionConfiguration, encryption at rest, peer TLS,
+  snapshot, backup, control plane. Do not use for broad cluster-wide CIS checks - use
+  performing-kubernetes-cis-benchmark-with-kube-bench.
 domain: cybersecurity
 subdomain: container-security
 tags: