fix: Default Tenant-ID in UCCA + Maximizer Proxies

Die UCCA Assessment Proxies leiteten X-Tenant-ID nur weiter wenn
der Browser ihn explizit sendete. Da das Frontend den Header nicht
setzt, kam immer 400/leer zurueck. Alle anderen Proxies (compliance,
training, academy etc.) hatten bereits den Fallback auf DEFAULT_TENANT_ID.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

admin-compliance/app/api/sdk/v1/ucca/assessments/route.ts

@@ -1,6 +1,7 @@
 import { NextRequest, NextResponse } from 'next/server'
 
 const SDK_URL = process.env.SDK_URL || 'http://ai-compliance-sdk:8090'
+const DEFAULT_TENANT_ID = process.env.DEFAULT_TENANT_ID || '9282a473-5c95-4b3a-bf78-0ecc0ec71d3e'
 
 /**
  * Proxy: GET /api/sdk/v1/ucca/assessments → Go Backend GET /sdk/v1/ucca/assessments
@@ -22,9 +23,7 @@ export async function GET(request: NextRequest) {
       method: 'GET',
       headers: {
         'Content-Type': 'application/json',
-        ...(request.headers.get('X-Tenant-ID') && {
-          'X-Tenant-ID': request.headers.get('X-Tenant-ID') as string,
-        }),
+        'X-Tenant-ID': request.headers.get('X-Tenant-ID') || DEFAULT_TENANT_ID,
       },
     })