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/implementing-opa-gatekeeper-for-policy-enforcement/SKILL.md

@@ -1,10 +1,14 @@
 ---
 name: implementing-opa-gatekeeper-for-policy-enforcement
-description: Deploys OPA Gatekeeper via Helm as a Kubernetes admission controller and writes
-  ConstraintTemplates with Rego rules plus instantiated Constraints to validate,
-  mutate, or deny resource requests at admission time. Use when enforcing policy-as-code
-  admission control in a Kubernetes cluster (v1.24+), such as blocking non-compliant
-  workloads before they are scheduled.
+description: >-
+  Deploys OPA Gatekeeper via Helm as a Kubernetes admission controller and writes
+  ConstraintTemplates with Rego plus instantiated Constraints to validate, mutate, or deny
+  resource requests at admission time. Use when enforcing custom policy-as-code at admission
+  on Kubernetes v1.24+, blocking non-compliant workloads before scheduling, or expressing a
+  rule that built-in controls cannot. Keywords: Gatekeeper, ConstraintTemplate, Constraint,
+  Rego, admission webhook, audit, mutation. Do not use for the standard pod security profiles
+  that Pod Security Admission already covers - use
+  implementing-pod-security-admission-controller.
 domain: cybersecurity
 subdomain: container-security
 tags: