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-user-behavior-analytics/SKILL.md

@@ -1,9 +1,10 @@
 ---
 name: performing-user-behavior-analytics
-description: 'Performs User and Entity Behavior Analytics (UEBA) to detect anomalous user activities including impossible
-  travel, unusual access patterns, privilege abuse, and insider threats using SIEM-based behavioral baselines and statistical
-  analysis. Use when SOC teams need to identify compromised accounts or insider threats through deviation from established
-  behavioral norms.
+description: 'Performs User and Entity Behavior Analytics (UEBA) to detect anomalous
+  user activities including impossible travel, unusual access patterns, privilege
+  abuse, and insider threats using SIEM-based behavioral baselines and statistical
+  analysis. Use when SOC teams need to identify compromised accounts or insider threats
+  through deviation from established behavioral norms.
 
   '
 domain: cybersecurity
@@ -24,6 +25,12 @@ nist_csf:
 - DE.AE-02
 - RS.MA-01
 - DE.AE-06
+mitre_attack:
+- T1078
+- T1685.002
+- T1685.005
+- T1566
+- T0816
 ---
 # Performing User Behavior Analytics