Map all 754 skills to MITRE ATT&CK v19.1

- Add validated mitre_attack frontmatter to all 754 skills (286 distinct
  techniques), verified against MITRE ATT&CK v19.1 via the official
  mitreattack-python library: 0 revoked, deprecated, or invalid IDs
- Curate precise per-skill technique IDs for forensics, malware-analysis,
  threat-intel, and red-team skills (e.g. DCSync -> T1003.006,
  Kerberoasting -> T1558.003, Pass-the-Ticket -> T1550.003)
- Reconcile v19.1 tactic restructuring: Defense Evasion split into
  Stealth (TA0005) and Defense Impairment (TA0112); revoked T1562.*
  family and T1070.001/.002 remapped to active equivalents (T1685.*)
- Normalize word-split tags across 35 skills (remove filename-derived
  stopword tags, add semantic cybersecurity tags)
- Add api-reference.md for 3 skills that were missing it
- Update README ATT&CK section with accurate v19.1 tactic distribution

skills/performing-supply-chain-attack-simulation/SKILL.md

@@ -1,7 +1,8 @@
 ---
 name: performing-supply-chain-attack-simulation
-description: Simulate and detect software supply chain attacks including typosquatting detection via Levenshtein distance,
-  dependency confusion testing against private registries, package hash verification with pip, and known vulnerability scanning
+description: Simulate and detect software supply chain attacks including typosquatting
+  detection via Levenshtein distance, dependency confusion testing against private
+  registries, package hash verification with pip, and known vulnerability scanning
   with pip-audit.
 domain: cybersecurity
 subdomain: application-security
@@ -21,6 +22,12 @@ nist_csf:
 - PR.PS-04
 - ID.RA-01
 - PR.DS-10
+mitre_attack:
+- T1078
+- T1190
+- T1059
+- T1195
+- T1554
 ---
 
 # Performing Supply Chain Attack Simulation