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/src/modules/classes/lib/notify.ts

@@ -0,0 +1,91 @@
+import { AttendanceStatus } from '@generated/prisma/client';
+import type { NotifyAbsenceResult, ProblemDetails, Result } from '@gruperly/shared';
+import { err, ok } from '@gruperly/shared';
+import { notFoundResourceProblem, validationProblem } from '@/http/problem-builders';
+import type { UnitOfWork } from '@/lib/prisma';
+import { type ClassesDb, sessionNotFound } from './helpers';
+
+type RegisterAbsenceDeps = {
+  db: Pick<ClassesDb, 'classSession' | 'attendee'>;
+  unitOfWork: UnitOfWork;
+};
+
+type RegisterAbsenceInput = {
+  attendeeId: string;
+  classSessionId: string;
+  now: Date;
+  releaseHours: number;
+};
+
+// Núcleo compartido del aviso de ausencia (profesor autenticado y alumno con token):
+// - Marca la asistencia como EXCUSED (upsert idempotente).
+// - Si la anticipación alcanza `releaseHours`, crea/conserva un SlotRelease para liberar el cupo.
+export async function registerAbsence(
+  deps: RegisterAbsenceDeps,
+  input: RegisterAbsenceInput,
+): Promise<Result<NotifyAbsenceResult, ProblemDetails>> {
+  const { db, unitOfWork } = deps;
+  const { attendeeId, classSessionId, now, releaseHours } = input;
+
+  const session = await db.classSession.findUnique({ where: { id: classSessionId } });
+  if (!session) {
+    return err(sessionNotFound(classSessionId));
+  }
+
+  const attendee = await db.attendee.findUnique({ where: { id: attendeeId } });
+  if (!attendee) {
+    return err(notFoundResourceProblem('Attendee', attendeeId));
+  }
+  if (attendee.groupId !== session.groupId) {
+    return err(
+      validationProblem({ detail: 'El alumno no pertenece al grupo de esta clase.' }),
+    );
+  }
+
+  const anticipationMs = session.startsAt.getTime() - now.getTime();
+  const slotReleased = anticipationMs >= releaseHours * 60 * 60 * 1000;
+
+  return unitOfWork.executeResult(async (tx) => {
+    await tx.attendance.upsert({
+      where: {
+        attendeeId_classSessionId: {
+          attendeeId,
+          classSessionId,
+        },
+      },
+      create: {
+        attendeeId,
+        classSessionId,
+        status: AttendanceStatus.EXCUSED,
+        markedAt: now,
+      },
+      update: {
+        status: AttendanceStatus.EXCUSED,
+        markedAt: now,
+      },
+    });
+
+    if (slotReleased) {
+      await tx.slotRelease.upsert({
+        where: {
+          attendeeId_classSessionId: {
+            attendeeId,
+            classSessionId,
+          },
+        },
+        create: {
+          attendeeId,
+          classSessionId,
+          isClaimed: false,
+        },
+        update: {},
+      });
+    }
+
+    return ok({
+      classSessionId,
+      notified: true,
+      slotReleased,
+    });
+  });
+}