feat: add absence notification and analytics features

- Implemented AbsenceNotifyView for notifying absence with session details.
- Created AnalyticsView for displaying group analytics and managing students at risk.
- Added ClassAttendanceView for marking attendance in classes.
- Defined new schemas for analytics and attendance in shared package.

apps/backend/prisma/models/domain.prisma

@@ -20,6 +20,7 @@ model Group {
   attendees Attendee[]
   payments  Payment[]
   waitlist  GroupWaitlistEntry[]
+  classSessions ClassSession[]
 
   @@map("groups")
 }
@@ -59,8 +60,14 @@ enum Role {
   MEMBER
 }
 
+enum AttendeeStatus {
+  ACTIVE
+  PAUSED
+  DROPPED
+}
+
 model Attendee {
-  id            String   @id @default(cuid())
+  id            String         @id @default(cuid())
   groupId       String
   fullName      String
   email         String?
@@ -68,11 +75,15 @@ model Attendee {
   guardianName  String?
   guardianPhone String?
   notes         String?
-  createdAt     DateTime @default(now())
-  updatedAt     DateTime @updatedAt
+  notifyToken   String?        @unique @default(cuid())
+  status        AttendeeStatus @default(ACTIVE)
+  createdAt     DateTime       @default(now())
+  updatedAt     DateTime       @updatedAt
 
-  group    Group    @relation(fields: [groupId], references: [id], onDelete: Cascade)
-  payments Payment[]
+  group        Group         @relation(fields: [groupId], references: [id], onDelete: Cascade)
+  payments     Payment[]
+  attendances  Attendance[]
+  slotReleases SlotRelease[]
 
   @@index([groupId])
   @@map("attendees")