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-gcp-vpc-firewall-rules/SKILL.md

@@ -1,15 +1,27 @@
 ---
 name: implementing-gcp-vpc-firewall-rules
-description: >
-  Implementing and auditing GCP VPC firewall rules to enforce network segmentation,
-  restrict ingress and egress traffic, apply hierarchical firewall policies across
-  the organization, and monitor firewall rule effectiveness using VPC Flow Logs.
+description: 'Implementing and auditing GCP VPC firewall rules to enforce network segmentation, restrict ingress and egress
+  traffic, apply hierarchical firewall policies across the organization, and monitor firewall rule effectiveness using VPC
+  Flow Logs.
+
+  '
 domain: cybersecurity
 subdomain: cloud-security
-tags: [cloud-security, gcp, vpc, firewall-rules, network-security, segmentation]
-version: "1.0"
+tags:
+- cloud-security
+- gcp
+- vpc
+- firewall-rules
+- network-security
+- 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 GCP VPC Firewall Rules