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/implementing-ransomware-backup-strategy/SKILL.md

@@ -1,10 +1,12 @@
 ---
 name: implementing-ransomware-backup-strategy
-description: 'Designs and implements a ransomware-resilient backup strategy following the 3-2-1-1-0 methodology (3 copies,
-  2 media types, 1 offsite, 1 immutable/air-gapped, 0 errors on restore verification). Configures backup schedules aligned
-  to RPO/RTO requirements, implements backup credential isolation to prevent ransomware from compromising backup infrastructure,
-  and establishes automated restore testing. Activates for requests involving ransomware backup planning, backup resilience,
-  air-gapped backup design, or backup recovery point objective configuration.
+description: 'Designs and implements a ransomware-resilient backup strategy following
+  the 3-2-1-1-0 methodology (3 copies, 2 media types, 1 offsite, 1 immutable/air-gapped,
+  0 errors on restore verification). Configures backup schedules aligned to RPO/RTO
+  requirements, implements backup credential isolation to prevent ransomware from
+  compromising backup infrastructure, and establishes automated restore testing. Activates
+  for requests involving ransomware backup planning, backup resilience, air-gapped
+  backup design, or backup recovery point objective configuration.
 
   '
 domain: cybersecurity
@@ -34,6 +36,12 @@ nist_csf:
 - RS.MA-01
 - RC.RP-01
 - PR.IR-01
+mitre_attack:
+- T1078
+- T1190
+- T1059
+- T1003
+- T1110
 ---
 # Implementing Ransomware Backup Strategy