improvement: task assignment notif added to notifications feature.

backend/prisma/migrations/20260718180000_lab_case_activity_task_assigned/migration.sql

@@ -0,0 +1,2 @@
+-- AlterEnum
+ALTER TYPE "LabCaseActivityType" ADD VALUE 'TASK_ASSIGNED';

backend/prisma/schema.prisma

@@ -429,6 +429,7 @@ enum LabCaseActivityType {
   CASE_IMPORTANT
   CASE_AMENDED
   TASK_COMPLETED
+  TASK_ASSIGNED
 }
 
 enum LabCaseTabReadTarget {