feat: initialize monorepo structure with Bun and Turborepo

- Add package.json for the root with workspace configuration and scripts
- Create @gruperly/config package with TypeScript configuration
- Establish shared package @gruperly/shared with Zod schemas for validation
- Implement group, student, and payment schemas using Zod
- Set up TypeScript configuration for shared package
- Document stack architecture and technical specifications in stack.md
- Configure Turborepo with build, dev, lint, and typecheck tasks

apps/api/prisma/schema.prisma

@@ -0,0 +1,171 @@
+// Gruperly - Prisma Schema (PostgreSQL)
+
+generator client {
+  provider = "prisma-client-js"
+}
+
+datasource db {
+  provider = "postgresql"
+  url      = env("DATABASE_URL")
+}
+
+// Auth (Better Auth) - required tables
+model User {
+  id             String    @id @default(cuid())
+  name           String
+  email          String    @unique
+  emailVerified  Boolean   @default(false)
+  image          String?
+  createdAt      DateTime  @default(now())
+  updatedAt      DateTime  @updatedAt
+
+  accounts Account[]
+  sessions Session[]
+  groupsMember   Member[]
+  groupsOwner    Group[]      @relation("OwnerGroups")
+  waitlist       WaitlistEntry[]
+}
+
+model Account {
+  id                String  @id @default(cuid())
+  userId            String
+  providerId        String
+  providerAccountId String
+  refreshToken      String?
+  accessToken       String?
+  accessTokenExpiresAt DateTime?
+  refreshTokenExpiresAt DateTime?
+  scope             String?
+  idToken           String?
+  password          String?
+  createdAt         DateTime @default(now())
+  updatedAt         DateTime @updatedAt
+
+  user User @relation(fields: [userId], references: [id], onDelete: Cascade)
+
+  @@unique([providerId, providerAccountId])
+}
+
+model Session {
+  id        String   @id @default(cuid())
+  userId    String
+  token     String   @unique
+  expiresAt DateTime
+  ipAddress String?
+  userAgent String?
+  createdAt DateTime @default(now())
+  updatedAt DateTime @updatedAt
+
+  user User @relation(fields: [userId], references: [id], onDelete: Cascade)
+}
+
+model Verification {
+  id         String   @id @default(cuid())
+  identifier String
+  value      String
+  expiresAt  DateTime
+  createdAt  DateTime @default(now())
+  updatedAt  DateTime @updatedAt
+
+  @@unique([identifier, value])
+}
+
+// Domain models
+model Group {
+  id          String   @id @default(cuid())
+  name        String
+  description String?
+  createdById String
+  createdAt   DateTime @default(now())
+  updatedAt   DateTime @updatedAt
+
+  owner    User     @relation("OwnerGroups", fields: [createdById], references: [id], onDelete: Cascade)
+  members  Member[]
+  students Student[]
+  payments Payment[]
+}
+
+model Member {
+  id      String @id @default(cuid())
+  groupId String
+  userId  String
+  role    Role   @default(MEMBER) // OWNER, ADMIN, MEMBER
+  joinedAt DateTime @default(now())
+
+  group Group @relation(fields: [groupId], references: [id], onDelete: Cascade)
+  user  User  @relation(fields: [userId], references: [id], onDelete: Cascade)
+
+  @@unique([groupId, userId])
+}
+
+enum Role {
+  OWNER
+  ADMIN
+  MEMBER
+}
+
+model Student {
+  id        String   @id @default(cuid())
+  groupId   String
+  fullName  String
+  email     String?
+  phone     String?
+  guardianName String?
+  guardianPhone String?
+  notes     String?
+  createdAt DateTime @default(now())
+  updatedAt DateTime @updatedAt
+
+  group    Group    @relation(fields: [groupId], references: [id], onDelete: Cascade)
+  payments Payment[]
+
+  @@index([groupId])
+}
+
+model Payment {
+  id        String        @id @default(cuid())
+  groupId   String
+  studentId String
+  amount    Decimal       @db.Decimal(10, 2)
+  currency  String        @default("MXN")
+  status    PaymentStatus @default(PENDING) // PENDING, PAID, OVERDUE, CANCELLED
+  dueDate   DateTime
+  paidAt    DateTime?
+  createdAt DateTime      @default(now())
+  updatedAt DateTime      @updatedAt
+
+  group   Group   @relation(fields: [groupId], references: [id], onDelete: Cascade)
+  student Student @relation(fields: [studentId], references: [id], onDelete: Cascade)
+
+  @@index([groupId])
+  @@index([studentId])
+}
+
+enum PaymentStatus {
+  PENDING
+  PAID
+  OVERDUE
+  CANCELLED
+}
+
+model WaitlistEntry {
+  id        String   @id @default(cuid())
+  email     String
+  name      String?
+  status    WaitlistStatus @default(PENDING) // PENDING, INVITED, JOINED, DECLINED
+  createdAt DateTime @default(now())
+  updatedAt DateTime @updatedAt
+
+  userId String? @unique
+
+  user User? @relation(fields: [userId], references: [id], onDelete: SetNull)
+
+  @@unique([email])
+}
+
+enum WaitlistStatus {
+  PENDING
+  INVITED
+  JOINED
+  DECLINED
+}