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-privilege-escalation-on-linux/SKILL.md

@@ -1,7 +1,8 @@
 ---
 name: performing-privilege-escalation-on-linux
-description: Linux privilege escalation involves elevating from a low-privilege user account to root access on a compromised
-  system. Red teams exploit misconfigurations, vulnerable services, kernel exploits, and w
+description: Linux privilege escalation involves elevating from a low-privilege user
+  account to root access on a compromised system. Red teams exploit misconfigurations,
+  vulnerable services, kernel exploits, and w
 domain: cybersecurity
 subdomain: red-teaming
 tags:
@@ -25,6 +26,12 @@ nist_csf:
 - ID.RA-01
 - GV.OV-02
 - DE.AE-07
+mitre_attack:
+- T1595
+- T1190
+- T1059
+- T1078
+- T1068
 ---
 # Performing Privilege Escalation on Linux