improvement: users get notified whenever a task is done completely, not per step.

backend/prisma/migrations/20260907200000_case_completed_notifications/migration.sql

@@ -0,0 +1,8 @@
+-- AlterEnum
+ALTER TYPE "LabCaseActivityType" ADD VALUE 'CASE_COMPLETED';
+
+-- AlterEnum
+ALTER TYPE "UserNotificationType" ADD VALUE 'CASE_COMPLETED';
+
+-- Step-level TASK_COMPLETED inbox rows were spam; case-complete uses CASE_COMPLETED going forward.
+DELETE FROM "UserNotification" WHERE type = 'TASK_COMPLETED';