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-active-directory-certificate-services-esc1/SKILL.md

@@ -1,12 +1,26 @@
 ---
 name: exploiting-active-directory-certificate-services-esc1
-description: Exploit misconfigured Active Directory Certificate Services (AD CS) ESC1 vulnerability to request certificates as high-privileged users and escalate domain privileges during authorized red team assessments.
+description: Exploit misconfigured Active Directory Certificate Services (AD CS) ESC1 vulnerability to request certificates
+  as high-privileged users and escalate domain privileges during authorized red team assessments.
 domain: cybersecurity
 subdomain: red-teaming
-tags: [red-team, active-directory, ad-cs, esc1, certificate-abuse, privilege-escalation, domain-escalation]
-version: "1.0"
+tags:
+- red-team
+- active-directory
+- ad-cs
+- esc1
+- certificate-abuse
+- privilege-escalation
+- domain-escalation
+version: '1.0'
 author: mahipal
 license: Apache-2.0
+d3fend_techniques:
+- File Metadata Consistency Validation
+- Certificate Analysis
+- Content Format Conversion
+- File Content Analysis
+- Platform Hardening
 ---
 # Exploiting Active Directory Certificate Services ESC1