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/detecting-attacks-on-historian-servers/SKILL.md

@@ -1,9 +1,11 @@
 ---
 name: detecting-attacks-on-historian-servers
-description: 'Detect cyber attacks targeting OT historian servers (OSIsoft PI, Ignition,
-  Wonderware) that sit at the IT/OT boundary and serve as pivot points for lateral
-  movement between enterprise and control networks, including data manipulation, unauthorized
-  queries, and exploitation of historian-specific vulnerabilities.
+description: 'Detect cyber attacks on OT historian servers (OSIsoft PI, Ignition, GE
+  Proficy, Wonderware InSQL) using a Python detector that flags unauthorized queries,
+  data manipulation, and lateral-movement indicators as historians pivot between IT
+  and OT networks. Use when monitoring historians bridging IT/OT zones for compromise,
+  investigating historian-specific CVE exploitation, or validating historian data integrity
+  after a suspected OT incident.
 
   '
 domain: cybersecurity