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/exploiting-ipv6-vulnerabilities/SKILL.md

@@ -1,15 +1,25 @@
 ---
 name: exploiting-ipv6-vulnerabilities
-description: >
-  Identifies and exploits IPv6-specific vulnerabilities including SLAAC spoofing,
-  Router Advertisement flooding, and IPv6 tunneling during authorized assessments
-  to test dual-stack security controls and IPv6-aware network defenses.
+description: 'Identifies and exploits IPv6-specific vulnerabilities including SLAAC spoofing, Router Advertisement flooding,
+  and IPv6 tunneling during authorized assessments to test dual-stack security controls and IPv6-aware network defenses.
+
+  '
 domain: cybersecurity
 subdomain: network-security
-tags: [network-security, ipv6, slaac, router-advertisement, dual-stack-security]
-version: "1.0"
+tags:
+- network-security
+- ipv6
+- slaac
+- router-advertisement
+- dual-stack-security
+version: '1.0'
 author: mahipal
 license: Apache-2.0
+nist_csf:
+- PR.IR-01
+- DE.CM-01
+- ID.AM-03
+- PR.DS-02
 ---
 # Exploiting IPv6 Vulnerabilities