feat: manage waitlist and remove group members

- Add group-waitlist module (list/promote/remove entries)
- Remove attendee with optional atomic promotion from waitlist
- Block removal when attendee has payments (attendee_has_payments)
- Waitlist detail modal matching members UI; optimistic add-to-waitlist
- Responsive tweaks for the members/waitlist tabs

apps/backend/src/modules/group-waitlist/lib/promote.ts

@@ -0,0 +1,83 @@
+import type { PrismaClient } from '@generated/prisma/client';
+import type { AttendeeDto, ProblemDetails, Result } from '@gruperly/shared';
+import { err, ok } from '@gruperly/shared';
+import { capacityReachedProblem, conflictProblem } from '@/http/problem-builders';
+import { type AttendeeRecord, toAttendeeDto } from '@/modules/attendees/lib/helpers';
+import { type GroupWaitlistEntryRecord } from './helpers';
+
+export type PromoteDb = Pick<PrismaClient, 'attendee' | 'groupWaitlistEntry'>;
+
+type PromoteGroup = {
+  id: string;
+  capacity: number | null;
+};
+
+export async function findFirstPendingWaitlistEntry(
+  db: PromoteDb,
+  groupId: string,
+): Promise<GroupWaitlistEntryRecord | null> {
+  const record = await db.groupWaitlistEntry.findFirst({
+    where: { groupId, status: 'PENDING' },
+    orderBy: { createdAt: 'asc' },
+  });
+  return record as GroupWaitlistEntryRecord | null;
+}
+
+export async function promoteWaitlistEntryRecord(
+  db: PromoteDb,
+  group: PromoteGroup,
+  entry: GroupWaitlistEntryRecord,
+): Promise<Result<AttendeeDto, ProblemDetails>> {
+  if (group.capacity !== null) {
+    const currentCount = await db.attendee.count({ where: { groupId: group.id } });
+    if (currentCount >= group.capacity) {
+      return err(capacityReachedProblem(group.capacity));
+    }
+  }
+
+  const existing = await db.attendee.findFirst({
+    where: { groupId: group.id, phone: entry.phone },
+  });
+  if (existing) {
+    return err(
+      conflictProblem({
+        detail: 'Ya existe un alumno registrado con este número de teléfono en este grupo.',
+        code: 'attendee_already_registered',
+      }),
+    );
+  }
+
+  const attendee = await db.attendee.create({
+    data: {
+      groupId: group.id,
+      fullName: entry.fullName,
+      phone: entry.phone,
+      email: entry.email,
+      notes: entry.notes,
+    },
+  });
+
+  return ok(toAttendeeDto(attendee as unknown as AttendeeRecord));
+}
+
+export type PromoteFirstResult = {
+  attendee: AttendeeDto;
+  entry: GroupWaitlistEntryRecord;
+};
+
+export async function promoteFirstPendingWaitlistEntry(
+  db: PromoteDb,
+  group: PromoteGroup,
+): Promise<Result<PromoteFirstResult | null, ProblemDetails>> {
+  const entry = await findFirstPendingWaitlistEntry(db, group.id);
+  if (!entry) {
+    return ok(null);
+  }
+
+  const result = await promoteWaitlistEntryRecord(db, group, entry);
+  if (!result.ok) {
+    return result;
+  }
+
+  return ok({ attendee: result.value, entry });
+}