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/testing-api-for-mass-assignment-vulnerability/SKILL.md

@@ -1,13 +1,10 @@
 ---
 name: testing-api-for-mass-assignment-vulnerability
-description: 'Tests APIs for mass assignment (auto-binding) vulnerabilities where
-  clients can modify object properties they should not have access to by including
-  additional parameters in API requests. The tester identifies writable endpoints,
-  adds undocumented fields to request bodies (role, isAdmin, price, balance), and
-  checks if the server binds these to the data model without filtering. Part of OWASP
-  API3:2023 Broken Object Property Level Authorization. Activates for requests involving
-  mass assignment testing, parameter binding abuse, auto-binding vulnerability, or
-  API over-posting.
+description: 'Tests APIs for mass assignment (auto-binding), OWASP API3:2023, by identifying
+  writable endpoints, adding undocumented fields to request bodies (role, isAdmin,
+  price, balance), and checking whether the server binds them to the data model without
+  filtering. Use when testing an API for mass assignment, parameter binding abuse,
+  or over-posting on profile, registration, or object-creation endpoints.
 
   '
 domain: cybersecurity