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-end-to-end-encryption-for-messaging/SKILL.md

@@ -1,12 +1,22 @@
 ---
 name: implementing-end-to-end-encryption-for-messaging
-description: End-to-end encryption (E2EE) ensures that only the communicating parties can read messages, with no intermediary (including the server) able to decrypt them. This skill implements a simplified version
+description: End-to-end encryption (E2EE) ensures that only the communicating parties can read messages, with no intermediary
+  (including the server) able to decrypt them. This skill implements a simplified version
 domain: cybersecurity
 subdomain: cryptography
-tags: [cryptography, encryption, e2e, messaging, signal-protocol]
-version: "1.0"
+tags:
+- cryptography
+- encryption
+- e2e
+- messaging
+- signal-protocol
+version: '1.0'
 author: mahipal
 license: Apache-2.0
+nist_csf:
+- PR.DS-01
+- PR.DS-02
+- PR.DS-10
 ---
 # Implementing End-to-End Encryption for Messaging