Rewrite 548 skill descriptions to the activation rubric

Each rewritten description now states both what the skill does (concrete
capability, named tools/artifacts) and an explicit when-to-use trigger,
improving agent discovery/activation. Grounded in each skill's own body;
changes confined to the `description` field only (bodies and all other
frontmatter untouched). Produced by a gated audit->rewrite->recheck loop
(548 -> 0 flagged) with a sampled anti-invention check (0 ungrounded).

Schema: 817/817 pass. Framework-ID gate: 0 defects.

skills/implementing-beyondcorp-zero-trust-access-model/SKILL.md

@@ -1,9 +1,11 @@
 ---
 name: implementing-beyondcorp-zero-trust-access-model
-description: 'Implementing Google''s BeyondCorp zero trust access model to eliminate
-  implicit trust from the network perimeter, enforce identity-aware access controls
-  using IAP, Access Context Manager, and Chrome Enterprise Premium for VPN-less secure
-  application access.
+description: 'Implement Google''s BeyondCorp zero trust access model using Cloud
+  IAP, Access Context Manager, Endpoint Verification, Chrome Enterprise Premium, and
+  BeyondCorp Enterprise Connectors to enforce identity- and device-aware access for
+  VPN-less application access. Use for replacing VPN, enforcing device posture checks,
+  or securing remote/hybrid access to GCP-hosted or on-prem apps; not for raw network-level
+  protocols.
 
   '
 domain: cybersecurity