fix(entity): appeler super.onCreate() dans SystemLog pour peupler dateCreation

Problème : SystemLog override @PrePersist sans appeler parent
Conséquence : dateCreation restait NULL → erreur PostgreSQL constraint violation
Solution : Ajout super.onCreate() pour déclencher BaseEntity.onCreate()

Fixes: null value in column date_creation violates not-null constraint

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/main/java/dev/lions/unionflow/server/entity/SystemLog.java

@@ -0,0 +1,98 @@
+package dev.lions.unionflow.server.entity;
+
+import jakarta.persistence.*;
+import lombok.Getter;
+import lombok.Setter;
+
+import java.time.LocalDateTime;
+
+/**
+ * Entité pour les logs techniques du système.
+ * Enregistre les erreurs, warnings, et événements système.
+ *
+ * @author UnionFlow Team
+ * @version 1.0
+ * @since 2026-03-15
+ */
+@Entity
+@Table(name = "system_logs", indexes = {
+    @Index(name = "idx_system_log_timestamp", columnList = "timestamp"),
+    @Index(name = "idx_system_log_level", columnList = "level"),
+    @Index(name = "idx_system_log_source", columnList = "source"),
+    @Index(name = "idx_system_log_user_id", columnList = "user_id")
+})
+@Getter
+@Setter
+public class SystemLog extends BaseEntity {
+
+    /**
+     * Niveau du log (CRITICAL, ERROR, WARNING, INFO, DEBUG)
+     */
+    @Column(name = "level", nullable = false, length = 20)
+    private String level;
+
+    /**
+     * Source du log (Database, API, Auth, System, Cache, etc.)
+     */
+    @Column(name = "source", nullable = false, length = 100)
+    private String source;
+
+    /**
+     * Message principal du log
+     */
+    @Column(name = "message", nullable = false, length = 1000)
+    private String message;
+
+    /**
+     * Détails supplémentaires (stacktrace, contexte, etc.)
+     */
+    @Column(name = "details", columnDefinition = "TEXT")
+    private String details;
+
+    /**
+     * Date/heure du log
+     */
+    @Column(name = "timestamp", nullable = false)
+    private LocalDateTime timestamp;
+
+    /**
+     * Identifiant de l'utilisateur concerné (optionnel)
+     */
+    @Column(name = "user_id", length = 255)
+    private String userId;
+
+    /**
+     * Adresse IP de la requête (optionnel)
+     */
+    @Column(name = "ip_address", length = 45)
+    private String ipAddress;
+
+    /**
+     * Identifiant de session (optionnel)
+     */
+    @Column(name = "session_id", length = 255)
+    private String sessionId;
+
+    /**
+     * Endpoint HTTP concerné (optionnel)
+     */
+    @Column(name = "endpoint", length = 500)
+    private String endpoint;
+
+    /**
+     * Code de statut HTTP (optionnel)
+     */
+    @Column(name = "http_status_code")
+    private Integer httpStatusCode;
+
+    /**
+     * Initialisation automatique du timestamp
+     */
+    @PrePersist
+    protected void onCreate() {
+        super.onCreate(); // Appel du @PrePersist de BaseEntity (dateCreation, actif)
+        if (timestamp == null) {
+            timestamp = LocalDateTime.now();
+        }
+    }
+}