fix: avoid null bytea in audit search JPQL

Hibernate binds null String params as bytea, causing PostgreSQL
lower(bytea) error. Convert null search to empty string in service
layer, use empty-string check in JPQL instead of IS NULL.

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

src/main/java/net/siegeln/cameleer/saas/audit/AuditRepository.java

@@ -25,9 +25,9 @@ public interface AuditRepository extends JpaRepository<AuditEntity, UUID> {
           AND (:result IS NULL OR a.result = :result)
           AND (:from IS NULL OR a.createdAt >= :from)
           AND (:to IS NULL OR a.createdAt <= :to)
-          AND (:search IS NULL
-               OR LOWER(a.actorEmail) LIKE LOWER(CONCAT('%', COALESCE(:search, ''), '%'))
-               OR LOWER(a.resource) LIKE LOWER(CONCAT('%', COALESCE(:search, ''), '%')))
+          AND (:search = ''
+               OR LOWER(a.actorEmail) LIKE LOWER(CONCAT('%', :search, '%'))
+               OR LOWER(a.resource) LIKE LOWER(CONCAT('%', :search, '%')))
         ORDER BY a.createdAt DESC
         """)
     Page<AuditEntity> findFiltered(

src/main/java/net/siegeln/cameleer/saas/audit/AuditService.java

@@ -37,6 +37,7 @@ public class AuditService {
     public Page<AuditEntity> search(UUID tenantId, String action, String result,
                                      Instant from, Instant to, String search,
                                      Pageable pageable) {
-        return auditRepository.findFiltered(tenantId, action, result, from, to, search, pageable);
+        String safeSearch = (search != null && !search.isBlank()) ? search.trim() : "";
+        return auditRepository.findFiltered(tenantId, action, result, from, to, safeSearch, pageable);
     }
 }