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-fileless-attacks-on-endpoints/SKILL.md

@@ -1,9 +1,11 @@
 ---
 name: detecting-fileless-attacks-on-endpoints
-description: 'Detects fileless malware and in-memory attacks that execute entirely in RAM without writing persistent files
-  to disk, evading traditional antivirus. Use when building detections for PowerShell-based attacks, reflective DLL injection,
-  WMI persistence, and registry-resident malware. Activates for requests involving fileless malware detection, in-memory attacks,
-  PowerShell exploitation, or living-off-the-land techniques.
+description: 'Detects fileless malware and in-memory attacks that execute entirely
+  in RAM without writing persistent files to disk, evading traditional antivirus.
+  Use when building detections for PowerShell-based attacks, reflective DLL injection,
+  WMI persistence, and registry-resident malware. Activates for requests involving
+  fileless malware detection, in-memory attacks, PowerShell exploitation, or living-off-the-land
+  techniques.
 
   '
 domain: cybersecurity
@@ -22,6 +24,12 @@ nist_csf:
 - PR.PS-02
 - DE.CM-01
 - PR.IR-01
+mitre_attack:
+- T1055
+- T1547
+- T1059
+- T1036
+- T1053
 ---
 # Detecting Fileless Attacks on Endpoints