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-identity-verification-for-zero-trust/SKILL.md

@@ -1,12 +1,24 @@
 ---
 name: implementing-identity-verification-for-zero-trust
-description: Implement continuous identity verification for zero trust using phishing-resistant MFA (FIDO2/WebAuthn), risk-based conditional access, and identity governance aligned with the CISA Zero Trust Maturity Model.
+description: Implement continuous identity verification for zero trust using phishing-resistant MFA (FIDO2/WebAuthn), risk-based
+  conditional access, and identity governance aligned with the CISA Zero Trust Maturity Model.
 domain: cybersecurity
 subdomain: zero-trust-architecture
-tags: [zero-trust, identity, authentication, mfa, identity-verification]
-version: "1.0"
+tags:
+- zero-trust
+- identity
+- authentication
+- mfa
+- identity-verification
+version: '1.0'
 author: mahipal
 license: Apache-2.0
+atlas_techniques:
+- AML.T0052
+nist_ai_rmf:
+- GOVERN-1.1
+- GOVERN-1.7
+- MAP-1.1
 ---
 
 # Implementing Identity Verification for Zero Trust