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/securing-github-actions-workflows/SKILL.md

@@ -1,8 +1,10 @@
 ---
 name: securing-github-actions-workflows
-description: 'This skill covers hardening GitHub Actions workflows against supply chain attacks, credential theft, and privilege
-  escalation. It addresses pinning actions to SHA digests, minimizing GITHUB_TOKEN permissions, protecting secrets from exfiltration,
-  preventing script injection in workflow expressions, and implementing required reviewers for workflow changes.
+description: 'This skill covers hardening GitHub Actions workflows against supply
+  chain attacks, credential theft, and privilege escalation. It addresses pinning
+  actions to SHA digests, minimizing GITHUB_TOKEN permissions, protecting secrets
+  from exfiltration, preventing script injection in workflow expressions, and implementing
+  required reviewers for workflow changes.
 
   '
 domain: cybersecurity
@@ -22,6 +24,12 @@ nist_csf:
 - GV.SC-07
 - ID.IM-04
 - PR.PS-04
+mitre_attack:
+- T1195
+- T1554
+- T1059.004
+- T1068
+- T1548
 ---
 
 # Securing GitHub Actions Workflows