feat: Third-country transfer tab in Vendor Compliance module

New "Drittlandtransfers" tab in the Vendor Compliance sidebar:
- Aggregates all vendor processing locations with non-EU countries
- Traffic light system: green (EU/adequacy), yellow (SCC exists),
  red (no transfer mechanism)
- Stats cards: total, EU+adequate, third-country, action required
- Filter by status (all/OK/review/action required)
- Table with vendor name, country, mechanism, SCC status, TIA status
- "TIA erstellen" link to Document Generator for third-country vendors
- Help text explaining Schrems II / Art. 46 DSGVO requirements

Uses existing data model — no new API endpoints or DB tables needed:
- vendor_vendors.processingLocations (isEU, isAdequate)
- vendor_vendors.transferMechanisms
- vendor_contracts.documentType = 'SCC'

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

admin-compliance/app/sdk/vendor-compliance/layout.tsx

@@ -48,6 +48,15 @@ const navItems: NavItem[] = [
       </svg>
     ),
   },
+  {
+    href: '/sdk/vendor-compliance/transfers',
+    label: 'Drittlandtransfers',
+    icon: (
+      <svg className="w-5 h-5" fill="none" viewBox="0 0 24 24" stroke="currentColor">
+        <path strokeLinecap="round" strokeLinejoin="round" strokeWidth={2} d="M3.055 11H5a2 2 0 012 2v1a2 2 0 002 2 2 2 0 012 2v2.945M8 3.935V5.5A2.5 2.5 0 0010.5 8h.5a2 2 0 012 2 2 2 0 104 0 2 2 0 012-2h1.064M15 20.488V18a2 2 0 012-2h3.064M21 12a9 9 0 11-18 0 9 9 0 0118 0z" />
+      </svg>
+    ),
+  },
   {
     href: '/sdk/vendor-compliance/risks',
     label: 'Risiken',