fix(sdk)+docs: dsfa-visibleWhen Bug, training.md, index.md komplett

Fixes:
- types.ts: dsfa isOptional false→true + visibleWhen ergänzt
  (sichtbar nur bei Scope L2/L3/L4 oder dsfaRequired Hard-Trigger)
- dsfa war einziger Step mit fehlendem visibleWhen laut Plan

Docs:
- training.md: NEU — Training Engine (seq 4800), alle Endpoints,
  Rollenmatrix, KI-Inhalt, Quiz, TTS-Media, DB-Schema
- mkdocs.yml: Training Engine nav-Eintrag
- index.md: E-Mail-Templates (4350) + Training Engine (4800)
  in Modul-Tabelle + URL-Liste ergänzt

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

mkdocs.yml

@@ -91,6 +91,7 @@ nav:
       - Industry Compliance Ingestion: services/sdk-modules/industry-compliance-ingestion.md
       - IACE (CE-Risikobeurteilung): services/sdk-modules/iace.md
       - Obligations v2 (CP-OBL): services/sdk-modules/obligations.md
+      - Training Engine (CP-TRAIN): services/sdk-modules/training.md
   - Entwicklung:
     - Testing: development/testing.md
     - Dokumentation: development/documentation.md