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/configuring-oauth2-authorization-flow/SKILL.md

@@ -1,7 +1,8 @@
 ---
 name: configuring-oauth2-authorization-flow
-description: Configure secure OAuth 2.0 authorization flows including Authorization Code with PKCE, Client Credentials, and
-  Device Authorization Grant. This skill covers flow selection, PKCE implementation, token
+description: Configure secure OAuth 2.0 authorization flows including Authorization
+  Code with PKCE, Client Credentials, and Device Authorization Grant. This skill covers
+  flow selection, PKCE implementation, token
 domain: cybersecurity
 subdomain: identity-access-management
 tags:
@@ -21,6 +22,12 @@ nist_csf:
 - PR.AA-02
 - PR.AA-05
 - PR.AA-06
+mitre_attack:
+- T1528
+- T1550.001
+- T1539
+- T1606.001
+- T1212
 ---
 # Configuring OAuth 2.0 Authorization Flow