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/hardening-linux-endpoint-with-cis-benchmark/SKILL.md

@@ -1,17 +1,28 @@
 ---
 name: hardening-linux-endpoint-with-cis-benchmark
-description: >
-  Hardens Linux endpoints using CIS Benchmark recommendations for Ubuntu, RHEL, and CentOS
-  to reduce attack surface, enforce security baselines, and meet compliance requirements. Use
-  when deploying new Linux servers, remediating audit findings, or establishing security
-  baselines for Linux infrastructure. Activates for requests involving Linux hardening, CIS
-  benchmarks for Linux, server security baselines, or Linux configuration compliance.
+description: 'Hardens Linux endpoints using CIS Benchmark recommendations for Ubuntu, RHEL, and CentOS to reduce attack surface,
+  enforce security baselines, and meet compliance requirements. Use when deploying new Linux servers, remediating audit findings,
+  or establishing security baselines for Linux infrastructure. Activates for requests involving Linux hardening, CIS benchmarks
+  for Linux, server security baselines, or Linux configuration compliance.
+
+  '
 domain: cybersecurity
 subdomain: endpoint-security
-tags: [endpoint, hardening, linux-security, CIS-benchmark, Ubuntu, RHEL]
+tags:
+- endpoint
+- hardening
+- linux-security
+- CIS-benchmark
+- Ubuntu
+- RHEL
 version: 1.0.0
 author: mahipal
 license: Apache-2.0
+nist_csf:
+- PR.PS-01
+- PR.PS-02
+- DE.CM-01
+- PR.IR-01
 ---
 # Hardening Linux Endpoint with CIS Benchmark