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/building-attack-pattern-library-from-cti-reports/SKILL.md

@@ -1,12 +1,27 @@
 ---
 name: building-attack-pattern-library-from-cti-reports
-description: Extract and catalog attack patterns from cyber threat intelligence reports into a structured STIX-based library mapped to MITRE ATT&CK for detection engineering and threat-informed defense.
+description: Extract and catalog attack patterns from cyber threat intelligence reports into a structured STIX-based library
+  mapped to MITRE ATT&CK for detection engineering and threat-informed defense.
 domain: cybersecurity
 subdomain: threat-intelligence
-tags: [attack-pattern, cti-reports, mitre-attack, stix, detection-engineering, threat-intelligence, nlp, extraction]
-version: "1.0"
+tags:
+- attack-pattern
+- cti-reports
+- mitre-attack
+- stix
+- detection-engineering
+- threat-intelligence
+- nlp
+- extraction
+version: '1.0'
 author: mahipal
 license: Apache-2.0
+d3fend_techniques:
+- File Metadata Consistency Validation
+- Application Protocol Command Analysis
+- Identifier Analysis
+- Content Format Conversion
+- Message Analysis
 ---
 # Building Attack Pattern Library from CTI Reports