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/migrations/20260923172527_add_attendee_status/migration.sql

@@ -0,0 +1,5 @@
+-- CreateEnum
+CREATE TYPE "AttendeeStatus" AS ENUM ('ACTIVE', 'PAUSED', 'DROPPED');
+
+-- AlterTable
+ALTER TABLE "attendees" ADD COLUMN     "status" "AttendeeStatus" NOT NULL DEFAULT 'ACTIVE';