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/securing-historian-server-in-ot-environment/SKILL.md

@@ -1,11 +1,10 @@
 ---
 name: securing-historian-server-in-ot-environment
-description: 'This skill covers hardening and securing process historian servers (OSIsoft
-  PI, Honeywell PHD, GE Proficy, AVEVA Historian) in OT environments. It addresses
-  network placement across Purdue levels, access control for historian interfaces,
-  data replication through DMZ using data diodes or PI-to-PI connectors, SQL injection
-  prevention in historian queries, and integrity protection of process data used for
-  safety analysis, regulatory reporting, and process optimization.
+description: 'Audits and hardens process historian servers (OSIsoft PI, Honeywell PHD,
+  GE Proficy, AVEVA Historian) in OT environments: Purdue-level network placement,
+  interface access control, secure DMZ replication via data diodes or PI-to-PI connectors,
+  SQL injection prevention, and process data integrity. Use when auditing or hardening
+  a historian server, or designing secure OT-to-IT data replication through a DMZ.
 
   '
 domain: cybersecurity