fix(escalations): Tenant/User-ID Defaults + Routing-Klarheit

- escalations/route.ts: X-Tenant-Id + X-User-Id Default-Header ergaenzt,
  X-User-Id aus Request weitergeleitet
- escalation_routes.py: DEFAULT_TENANT_ID Konstante (9282a473-...) statt 'default'
- test_escalation_routes.py: vollstaendige Test-Suite ergaenzt (+337 Zeilen)
- main.go + escalation_handlers.go: DEPRECATED-Kommentare — UCCA-Escalations
  bleiben fuer Assessment-Review, Haupt-Escalation-System ist Python-Backend

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

ai-compliance-sdk/internal/api/handlers/escalation_handlers.go

@@ -1,3 +1,7 @@
+// DEPRECATED: This file implements UCCA-specific escalation handlers (E0-E3 workflow).
+// The primary escalation system is now Python backend-compliance escalation_routes.py
+// (/api/compliance/escalations). These UCCA handlers remain only for assessment-review
+// workflows and will be removed in a future release.
 package handlers
 
 import (