feat: add NIST CSF 2.0 nist_csf field to all 754 cybersecurity skills

Mapped every skill to NIST CSF 2.0 subcategory IDs (GV/ID/PR/DE/RS/RC functions)
based on subdomain and content analysis. Restores 11 skills corrupted during
prior rebase, re-enriching with ATLAS, D3FEND, NIST AI RMF, and CSF 2.0 fields.

All 754 skills now carry structured mappings for all 5 security frameworks:
- MITRE ATT&CK (in tags)
- MITRE ATLAS v5.5 (atlas_techniques)
- MITRE D3FEND v1.3 (d3fend_techniques)
- NIST AI RMF 1.0 (nist_ai_rmf)
- NIST CSF 2.0 (nist_csf)

skills/implementing-continuous-security-validation-with-bas/SKILL.md

@@ -22,6 +22,11 @@ d3fend_techniques:
 - Identifier Analysis
 - Content Format Conversion
 - Message Analysis
+nist_csf:
+- ID.RA-01
+- ID.RA-02
+- ID.IM-02
+- ID.RA-06
 ---
 # Implementing Continuous Security Validation with BAS