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-with-beyondcorp/SKILL.md

@@ -1,12 +1,25 @@
 ---
 name: implementing-zero-trust-with-beyondcorp
-description: Deploy Google BeyondCorp Enterprise zero trust access controls using Identity-Aware Proxy (IAP), context-aware access policies, device trust validation, and Access Context Manager to enforce identity and posture-based access to GCP resources and internal applications.
+description: Deploy Google BeyondCorp Enterprise zero trust access controls using Identity-Aware Proxy (IAP), context-aware
+  access policies, device trust validation, and Access Context Manager to enforce identity and posture-based access to GCP
+  resources and internal applications.
 domain: cybersecurity
 subdomain: zero-trust
-tags: [zero-trust, beyondcorp, google-cloud, iap, context-aware-access, device-trust, identity]
-version: "1.0"
+tags:
+- zero-trust
+- beyondcorp
+- google-cloud
+- iap
+- context-aware-access
+- device-trust
+- identity
+version: '1.0'
 author: mahipal
 license: Apache-2.0
+nist_csf:
+- PR.AA-01
+- PR.AA-05
+- PR.IR-01
 ---
 
 # Implementing Zero Trust with BeyondCorp