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-mitre-attack-coverage-mapping/SKILL.md

@@ -1,12 +1,33 @@
 ---
 name: implementing-mitre-attack-coverage-mapping
-description: Implement MITRE ATT&CK coverage mapping to identify detection gaps, prioritize rule development, and measure SOC detection maturity against adversary techniques.
+description: Implement MITRE ATT&CK coverage mapping to identify detection gaps, prioritize rule development, and measure
+  SOC detection maturity against adversary techniques.
 domain: cybersecurity
 subdomain: soc-operations
-tags: [mitre-attack, detection-coverage, gap-analysis, attack-navigator, soc, detection-engineering]
-version: "1.0"
+tags:
+- mitre-attack
+- detection-coverage
+- gap-analysis
+- attack-navigator
+- soc
+- detection-engineering
+version: '1.0'
 author: mahipal
 license: Apache-2.0
+nist_ai_rmf:
+- MEASURE-2.7
+- MAP-5.1
+- MANAGE-2.4
+atlas_techniques:
+- AML.T0070
+- AML.T0066
+- AML.T0082
+d3fend_techniques:
+- Token Binding
+- Restore Access
+- Application Protocol Command Analysis
+- Password Authentication
+- Reissue Credential
 ---
 
 # Implementing MITRE ATT&CK Coverage Mapping