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-zero-trust-dns-with-nextdns/SKILL.md

@@ -1,12 +1,27 @@
 ---
 name: implementing-zero-trust-dns-with-nextdns
-description: Implement NextDNS as a zero trust DNS filtering layer with encrypted resolution, threat intelligence blocking, privacy protection, and organizational policy enforcement across all endpoints.
+description: Implement NextDNS as a zero trust DNS filtering layer with encrypted resolution, threat intelligence blocking,
+  privacy protection, and organizational policy enforcement across all endpoints.
 domain: cybersecurity
 subdomain: zero-trust-architecture
-tags: [zero-trust, dns, nextdns, dns-over-https, dns-over-tls, threat-blocking, dns-filtering, privacy, encrypted-dns]
-version: "1.0"
+tags:
+- zero-trust
+- dns
+- nextdns
+- dns-over-https
+- dns-over-tls
+- threat-blocking
+- dns-filtering
+- privacy
+- encrypted-dns
+version: '1.0'
 author: mahipal
 license: Apache-2.0
+nist_csf:
+- PR.AA-01
+- PR.AA-05
+- PR.IR-01
+- GV.PO-01
 ---
 
 # Implementing Zero Trust DNS with NextDNS