fix: allow slug reuse after tenant soft-delete

existsBySlug found DELETED records, blocking slug reuse. Changed to
existsBySlugAndStatusNot(slug, DELETED) so deleted tenant slugs can
be reclaimed.

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

src/main/java/net/siegeln/cameleer/saas/tenant/TenantRepository.java

@@ -13,4 +13,5 @@ public interface TenantRepository extends JpaRepository<TenantEntity, UUID> {
     Optional<TenantEntity> findByLogtoOrgId(String logtoOrgId);
     List<TenantEntity> findByStatus(TenantStatus status);
     boolean existsBySlug(String slug);
+    boolean existsBySlugAndStatusNot(String slug, TenantStatus status);
 }

src/main/java/net/siegeln/cameleer/saas/tenant/TenantService.java

@@ -24,7 +24,7 @@ public class TenantService {
     }
 
     public TenantEntity create(CreateTenantRequest request, UUID actorId) {
-        if (tenantRepository.existsBySlug(request.slug())) {
+        if (tenantRepository.existsBySlugAndStatusNot(request.slug(), TenantStatus.DELETED)) {
             throw new IllegalArgumentException("Slug already taken");
         }