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/configuring-multi-factor-authentication-with-duo/SKILL.md

@@ -1,12 +1,25 @@
 ---
 name: configuring-multi-factor-authentication-with-duo
-description: Deploy Cisco Duo multi-factor authentication across enterprise applications, VPN, RDP, and SSH access points. This skill covers Duo integration methods, adaptive authentication policies, device trust 
+description: Deploy Cisco Duo multi-factor authentication across enterprise applications, VPN, RDP, and SSH access points.
+  This skill covers Duo integration methods, adaptive authentication policies, device trust
 domain: cybersecurity
 subdomain: identity-access-management
-tags: [iam, identity, access-control, authentication, mfa, duo, multi-factor]
-version: "1.0"
+tags:
+- iam
+- identity
+- access-control
+- authentication
+- mfa
+- duo
+- multi-factor
+version: '1.0'
 author: mahipal
 license: Apache-2.0
+nist_csf:
+- PR.AA-01
+- PR.AA-02
+- PR.AA-05
+- PR.AA-06
 ---
 # Configuring Multi-Factor Authentication with Duo