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-for-saas-applications/SKILL.md

@@ -1,15 +1,28 @@
 ---
 name: implementing-zero-trust-for-saas-applications
-description: >
-  Implementing zero trust access controls for SaaS applications using CASB, SSPM,
-  conditional access policies, OAuth app governance, and session controls to enforce
-  identity verification, device compliance, and data protection for cloud-hosted services.
+description: 'Implementing zero trust access controls for SaaS applications using CASB, SSPM, conditional access policies,
+  OAuth app governance, and session controls to enforce identity verification, device compliance, and data protection for
+  cloud-hosted services.
+
+  '
 domain: cybersecurity
 subdomain: zero-trust-architecture
-tags: [zero-trust, saas-security, casb, sspm, conditional-access, oauth-governance, session-controls]
-version: "1.0"
+tags:
+- zero-trust
+- saas-security
+- casb
+- sspm
+- conditional-access
+- oauth-governance
+- session-controls
+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 for SaaS Applications