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-fileless-malware-techniques/SKILL.md

@@ -2,8 +2,8 @@
 name: detecting-fileless-malware-techniques
 description: 'Detects and analyzes fileless malware that operates entirely in memory
   using PowerShell, WMI, .NET reflection, registry-resident payloads, and living-off-the-land
-  binaries (LOLBins) without writing traditional executable files to disk. Activates
-  for requests involving fileless threat detection, in-memory malware investigation,
+  binaries (LOLBins) without writing traditional executable files to disk. Use for
+  requests involving fileless threat detection, in-memory malware investigation,
   LOLBin abuse analysis, or WMI persistence examination.
 
   '