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-siem-use-case-tuning/SKILL.md

@@ -1,19 +1,25 @@
 ---
 name: implementing-siem-use-case-tuning
-description: Tune SIEM detection rules to reduce false positives by analyzing alert volumes, creating whitelists, adjusting thresholds, and measuring detection efficacy metrics in Splunk and Elastic
+description: Tune SIEM detection rules to reduce false positives by analyzing alert volumes, creating whitelists, adjusting
+  thresholds, and measuring detection efficacy metrics in Splunk and Elastic
 domain: cybersecurity
 subdomain: security-operations
 tags:
-  - siem
-  - detection-engineering
-  - false-positive-reduction
-  - splunk
-  - elastic
-  - alert-tuning
-  - soc
-version: "1.0"
+- siem
+- detection-engineering
+- false-positive-reduction
+- splunk
+- elastic
+- alert-tuning
+- soc
+version: '1.0'
 author: mahipal
 license: Apache-2.0
+nist_csf:
+- DE.CM-01
+- RS.MA-01
+- GV.OV-01
+- DE.AE-02
 ---
 
 # Implementing SIEM Use Case Tuning