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/performing-false-positive-reduction-in-siem/SKILL.md

@@ -1,8 +1,9 @@
 ---
 name: performing-false-positive-reduction-in-siem
-description: Perform systematic SIEM false positive reduction through rule tuning,
-  threshold adjustment, correlation refinement, and threat intelligence enrichment
-  to combat alert fatigue.
+description: Reduces SIEM false positives through systematic rule tuning, threshold
+  adjustment, correlation logic refinement, allowlisting, and threat intelligence
+  enrichment. Use when SOC analysts are overwhelmed by alert noise, when tuning noisy
+  detection rules, or during a quarterly SIEM rule review to cut alert fatigue.
 domain: cybersecurity
 subdomain: soc-operations
 tags: