feature: version one notification feature implemented.

backend/prisma/schema.prisma

@@ -30,6 +30,8 @@ model User {
   labCaseComments LabCaseComment[]
   labCaseActivities LabCaseActivity[]
   phoneVerificationCodes PhoneVerificationCode[]
+  userNotifications UserNotification[]
+  actedUserNotifications UserNotification[] @relation("UserNotificationActor")
 
   createdAt DateTime @default(now())
   updatedAt DateTime @updatedAt
@@ -435,6 +437,38 @@ enum LabCaseTabReadTarget {
   TREATMENT
 }
 
+enum UserNotificationType {
+  CASE_SENT
+  CLINIC_COMMENT
+  LAB_COMMENT
+  LAB_COMMENT_CLINIC
+  CASE_IMPORTANT
+  TASK_COMPLETED
+  TASK_ASSIGNED
+  CONNECTION_REQUEST
+  STAFF_INVITE
+}
+
+/// Fan-out inbox row per recipient. Independent of LabCaseActivity tab badges.
+model UserNotification {
+  id             String               @id @default(uuid())
+  userId         String
+  organizationId String
+  type           UserNotificationType
+  actorUserId    String?
+  payload        Json?
+  href           String
+  readAt         DateTime?
+  createdAt      DateTime             @default(now())
+
+  user      User  @relation(fields: [userId], references: [id], onDelete: Cascade)
+  actorUser User? @relation("UserNotificationActor", fields: [actorUserId], references: [id], onDelete: SetNull)
+
+  @@index([userId, organizationId, createdAt])
+  @@index([userId, organizationId, readAt])
+  @@map("user_notifications")
+}
+
 model LabCaseActivity {
   id          String              @id @default(uuid())
   labCaseId   String