fix: resolve actor name from Logto for audit log entries

AuditService now looks up username/name/email from Logto Management API
when actorEmail is null, with an in-memory cache to avoid repeated calls.

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

src/test/java/net/siegeln/cameleer/saas/audit/AuditServiceTest.java

@@ -1,5 +1,6 @@
 package net.siegeln.cameleer.saas.audit;
 
+import net.siegeln.cameleer.saas.identity.LogtoManagementClient;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.extension.ExtendWith;
@@ -20,11 +21,14 @@ class AuditServiceTest {
     @Mock
     private AuditRepository auditRepository;
 
+    @Mock
+    private LogtoManagementClient logtoClient;
+
     private AuditService auditService;
 
     @BeforeEach
     void setUp() {
-        auditService = new AuditService(auditRepository);
+        auditService = new AuditService(auditRepository, logtoClient);
     }
 
     @Test