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-network-access/SKILL.md

@@ -1,16 +1,27 @@
 ---
 name: implementing-zero-trust-network-access
-description: >
-  Implementing Zero Trust Network Access (ZTNA) in cloud environments by configuring
-  identity-aware proxies, micro-segmentation, continuous verification with conditional
-  access policies, and replacing traditional VPN-based access with BeyondCorp-style
+description: 'Implementing Zero Trust Network Access (ZTNA) in cloud environments by configuring identity-aware proxies, micro-segmentation,
+  continuous verification with conditional access policies, and replacing traditional VPN-based access with BeyondCorp-style
   architectures across AWS, Azure, and GCP.
+
+  '
 domain: cybersecurity
 subdomain: cloud-security
-tags: [cloud-security, zero-trust, ztna, beyondcorp, identity-aware-proxy, micro-segmentation]
-version: "1.0"
+tags:
+- cloud-security
+- zero-trust
+- ztna
+- beyondcorp
+- identity-aware-proxy
+- micro-segmentation
+version: '1.0'
 author: mahipal
 license: Apache-2.0
+nist_csf:
+- PR.IR-01
+- ID.AM-08
+- GV.SC-06
+- DE.CM-01
 ---
 
 # Implementing Zero Trust Network Access