feat: enrich 209 skills with MITRE ATLAS, D3FEND, and NIST AI RMF frontmatter

Added structured security framework mappings to SKILL.md frontmatter across all applicable skills:
- atlas_techniques: MITRE ATLAS v5.5 AML.TXXXX IDs (81 skills, AI-targeted attack techniques)
- d3fend_techniques: MITRE D3FEND v1.3 defensive technique labels (139 skills, mapped from ATT&CK IDs)
- nist_ai_rmf: NIST AI RMF 1.0 subcategory IDs (85 skills, AI risk management functions)

Also updates ATTACK_COVERAGE.md with coverage statistics for all three frameworks.

skills/exploiting-constrained-delegation-abuse/SKILL.md

@@ -1,12 +1,26 @@
 ---
 name: exploiting-constrained-delegation-abuse
-description: Exploit Kerberos Constrained Delegation misconfigurations in Active Directory to impersonate privileged users via S4U2self and S4U2proxy extensions for lateral movement and privilege escalation.
+description: Exploit Kerberos Constrained Delegation misconfigurations in Active Directory to impersonate privileged users
+  via S4U2self and S4U2proxy extensions for lateral movement and privilege escalation.
 domain: cybersecurity
 subdomain: red-teaming
-tags: [red-team, active-directory, kerberos, constrained-delegation, s4u2proxy, privilege-escalation, lateral-movement]
-version: "1.0"
+tags:
+- red-team
+- active-directory
+- kerberos
+- constrained-delegation
+- s4u2proxy
+- privilege-escalation
+- lateral-movement
+version: '1.0'
 author: mahipal
 license: Apache-2.0
+d3fend_techniques:
+- Application Protocol Command Analysis
+- Network Isolation
+- Network Traffic Analysis
+- Client-server Payload Profiling
+- Network Traffic Community Deviation
 ---
 # Exploiting Constrained Delegation Abuse