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/scanning-docker-images-with-trivy/SKILL.md

@@ -1,11 +1,14 @@
 ---
 name: scanning-docker-images-with-trivy
-description: Scans Docker container images with Trivy, Aqua Security's open-source
-  scanner, to detect vulnerabilities in OS packages and language-specific dependencies,
-  misconfigurations, exposed secrets, and license violations, outputting results in
-  formats like SARIF, CycloneDX, or SPDX. Use when assessing, auditing, or scheduling
-  a security scan of Docker images, including as part of CI/CD or incident-response
-  investigations.
+description: >-
+  Scans a Docker image with Trivy for vulnerabilities in OS packages and language
+  dependencies, misconfiguration, exposed secrets, and licence violations, emitting SARIF,
+  CycloneDX, or SPDX output. Use when scanning or gating a specific image, wiring an image
+  scan into CI/CD, or checking an image during an incident investigation. Keywords: Trivy,
+  image scan, --severity, --exit-code, SARIF, ignore file, .trivyignore. Do not use for
+  cluster-wide scanning or non-image targets - use
+  performing-container-security-scanning-with-trivy; when the toolchain is Grype use
+  scanning-container-images-with-grype.
 domain: cybersecurity
 subdomain: container-security
 tags: