fix: exclude DELETED tenants from vendor tenant list

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

src/main/java/net/siegeln/cameleer/saas/vendor/VendorTenantService.java

@@ -98,7 +98,9 @@ public class VendorTenantService {
     }
 
     public List<TenantEntity> listAll() {
-        return tenantService.findAll();
+        return tenantService.findAll().stream()
+            .filter(t -> t.getStatus() != TenantStatus.DELETED)
+            .toList();
     }
 
     public Optional<TenantEntity> getById(UUID id) {