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/detecting-email-forwarding-rules-attack/SKILL.md

@@ -1,7 +1,7 @@
 ---
 name: detecting-email-forwarding-rules-attack
-description: Detect malicious email forwarding rules created by adversaries to maintain persistent access to email communications
-  for intelligence collection and BEC attacks.
+description: Detect malicious email forwarding rules created by adversaries to maintain
+  persistent access to email communications for intelligence collection and BEC attacks.
 domain: cybersecurity
 subdomain: threat-hunting
 tags:
@@ -26,6 +26,12 @@ nist_csf:
 - DE.AE-02
 - DE.AE-07
 - ID.RA-05
+mitre_attack:
+- T1046
+- T1057
+- T1082
+- T1083
+- T1547
 ---
 
 # Detecting Email Forwarding Rules Attack