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/implementing-cisa-zero-trust-maturity-model/SKILL.md

@@ -1,12 +1,30 @@
 ---
 name: implementing-cisa-zero-trust-maturity-model
-description: Implement the CISA Zero Trust Maturity Model v2.0 across the five pillars of identity, devices, networks, applications, and data to achieve progressive organizational zero trust maturity.
+description: Implement the CISA Zero Trust Maturity Model v2.0 across the five pillars of identity, devices, networks, applications,
+  and data to achieve progressive organizational zero trust maturity.
 domain: cybersecurity
 subdomain: zero-trust-architecture
-tags: [zero-trust, cisa, maturity-model, federal-compliance, governance, nist-800-207, identity, devices, networks, applications, data-security]
-version: "1.0"
+tags:
+- zero-trust
+- cisa
+- maturity-model
+- federal-compliance
+- governance
+- nist-800-207
+- identity
+- devices
+- networks
+- applications
+- data-security
+version: '1.0'
 author: mahipal
 license: Apache-2.0
+nist_ai_rmf:
+- GOVERN-1.1
+- GOVERN-1.7
+- MAP-1.1
+- GOVERN-4.2
+- MAP-2.3
 ---
 
 # Implementing CISA Zero Trust Maturity Model