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/conducting-post-incident-lessons-learned/SKILL.md

@@ -1,7 +1,8 @@
 ---
 name: conducting-post-incident-lessons-learned
-description: Facilitate structured post-incident reviews to identify root causes, document what worked and failed, and produce
-  actionable recommendations to improve future incident response.
+description: Facilitate structured post-incident reviews to identify root causes,
+  document what worked and failed, and produce actionable recommendations to improve
+  future incident response.
 domain: cybersecurity
 subdomain: incident-response
 tags:
@@ -11,8 +12,9 @@ tags:
 - after-action-review
 - process-improvement
 mitre_attack:
-- T1190
 - T1566
+- T1486
+- T1059
 - T1078
 version: '1.0'
 author: mahipal