fix: SystemAlert @PrePersist override + types_reference complete schema in V1

- SystemAlert.onCreate() now calls super.onCreate() to set dateCreation (was null → NOT NULL violation every minute)
- V1: types_reference updated with full schema (domaine, est_defaut, est_systeme, ordre_affichage, modules_requis, organisation_id)
- V9: idempotent guard for categorie nullable ALTER (already nullable in updated V1)

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

@@ -108,6 +108,7 @@ public class SystemAlert extends BaseEntity {
      */
     @PrePersist
     protected void onCreate() {
+        super.onCreate();
         if (timestamp == null) {
             timestamp = LocalDateTime.now();
         }