refactor: migrate backend to pnpm monorepo with Hono module architecture

- Replace Bun with pnpm 9 + Turborepo + tsx; apps/api renamed to apps/backend
- Split backend into http/, modules/, lib/ layers mirroring tai-specguard
- Add use-case + Result pattern, Problem Details RFC 7807, basePath /api/v1
- Mount Better Auth at /api/v1/auth, keep session-auth whitelist
- Split Prisma schema into prisma/models/*, generate into generated/
- Rework packages/shared into lib/ + schemas/ with pagination DTOs
- Implement health, groups, students, payments, waitlist modules
- Add vitest suite with prisma mocks (21 tests), biome lint
- Point web client to /api/v1/auth and /api/v1/groups/from-organization

apps/backend/src/lib/email.ts

@@ -0,0 +1,94 @@
+import nodemailer, { type Transporter } from 'nodemailer'
+
+type VerificationEmailData = { email: string; url: string; name?: string }
+type PasswordResetEmailData = { email: string; url: string; name?: string }
+type InvitationEmailData = { email: string; url: string; organizationName: string }
+
+interface EmailProvider {
+  sendVerificationEmail(data: VerificationEmailData): Promise<void>
+  sendPasswordResetEmail(data: PasswordResetEmailData): Promise<void>
+  sendOrganizationInvitation(data: InvitationEmailData): Promise<void>
+}
+
+class SMTPEmailProvider implements EmailProvider {
+  private transporter: Transporter
+
+  constructor() {
+    this.transporter = nodemailer.createTransport({
+      host: process.env.EMAIL_SERVER_HOST,
+      port: Number(process.env.EMAIL_SERVER_PORT ?? 587),
+      secure: (process.env.EMAIL_SERVER_PORT ?? '587') === '465',
+      auth: {
+        user: process.env.EMAIL_SERVER_USER,
+        pass: process.env.EMAIL_SERVER_PASSWORD,
+      },
+    })
+  }
+
+  private from() {
+    return process.env.EMAIL_FROM ?? 'Gruperly <no-reply@gruperly.com>'
+  }
+
+  private layout(title: string, body: string) {
+    return `
+      <div style="font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif; max-width: 480px; margin: 0 auto; padding: 24px; color: #0a2540;">
+        <h2 style="margin: 0 0 16px;">Gruperly</h2>
+        <h3 style="margin: 0 0 8px;">${title}</h3>
+        <p style="line-height: 1.6; color: #334155;">${body}</p>
+      </div>
+    `
+  }
+
+  private async send(to: string, subject: string, html: string) {
+    // Sin SMTP configurado (dev) no rompe el flujo: solo registra un aviso
+    if (!process.env.EMAIL_SERVER_HOST) {
+      console.warn(`[email] SMTP no configurado. Email no enviado a ${to}: "${subject}"`)
+      return
+    }
+    await this.transporter.sendMail({ from: this.from(), to, subject, html })
+  }
+
+  async sendVerificationEmail({ email, url, name }: VerificationEmailData) {
+    const link = `<a href="${url}" style="display:inline-block;background:#1e90ff;color:#fff;text-decoration:none;padding:12px 24px;border-radius:12px;font-weight:600;">Verificar email</a>`
+    await this.send(
+      email,
+      'Verifica tu email en Gruperly',
+      this.layout(
+        'Confirma tu dirección de email',
+        `${name ? `Hola ${name}, ` : 'Hola, '}gracias por crear tu cuenta en Gruperly. Para empezar, verifica tu email con el botón de abajo (el enlace vence en 1 hora).<br/><br/>${link}`,
+      ),
+    )
+  }
+
+  async sendPasswordResetEmail({ email, url, name }: PasswordResetEmailData) {
+    const link = `<a href="${url}" style="display:inline-block;background:#1e90ff;color:#fff;text-decoration:none;padding:12px 24px;border-radius:12px;font-weight:600;">Restablecer contraseña</a>`
+    await this.send(
+      email,
+      'Restablece tu contraseña en Gruperly',
+      this.layout(
+        'Solicitaste restablecer tu contraseña',
+        `${name ? `Hola ${name}, ` : 'Hola, '}haz clic en el botón para elegir una nueva contraseña (el enlace vence en 1 hora). Si no fuiste tú, ignora este email.<br/><br/>${link}`,
+      ),
+    )
+  }
+
+  async sendOrganizationInvitation({ email, url, organizationName }: InvitationEmailData) {
+    const link = `<a href="${url}" style="display:inline-block;background:#1e90ff;color:#fff;text-decoration:none;padding:12px 24px;border-radius:12px;font-weight:600;">Unirme a ${organizationName}</a>`
+    await this.send(
+      email,
+      `Te invitaron a ${organizationName} en Gruperly`,
+      this.layout(
+        `Te invitaron a ${organizationName}`,
+        `Acepta la invitación con el botón de abajo para empezar a colaborar en Gruperly.<br/><br/>${link}`,
+      ),
+    )
+  }
+}
+
+// Futuro: proveedores transaccionales (Resend, SendGrid, Postmark).
+// Añadir implementaciones y alternar con EMAIL_PROVIDER.
+export function createEmailProvider(): EmailProvider {
+  return new SMTPEmailProvider()
+}
+
+export const emailProvider = createEmailProvider()

apps/backend/src/lib/error-message.ts

@@ -0,0 +1,3 @@
+export function toErrorMessage(error: unknown): string {
+  return error instanceof Error ? error.message : String(error);
+}

apps/backend/src/lib/pagination.ts

@@ -0,0 +1,25 @@
+type PaginationInput = {
+  page: number;
+  pageSize: number;
+};
+
+type PaginationMetadata = PaginationInput & {
+  total: number;
+  totalPages: number;
+};
+
+export function getPaginationMetadata(
+  { page, pageSize }: PaginationInput,
+  total: number,
+): PaginationMetadata {
+  return {
+    page,
+    pageSize,
+    total,
+    totalPages: Math.ceil(total / pageSize),
+  };
+}
+
+export function getPaginationOffset({ page, pageSize }: PaginationInput): number {
+  return (page - 1) * pageSize;
+}

apps/backend/src/lib/prisma.ts

@@ -0,0 +1,72 @@
+import 'dotenv/config';
+import { type Prisma, PrismaClient } from '@generated/prisma/client';
+import type { Result } from '@gruperly/shared';
+import { PrismaPg } from '@prisma/adapter-pg';
+
+let prismaClient: PrismaClient | undefined;
+
+function createPrismaClient(): PrismaClient {
+  const databaseUrl = process.env.DATABASE_URL;
+  if (!databaseUrl) {
+    throw new Error('DATABASE_URL environment variable is required');
+  }
+
+  return new PrismaClient({
+    adapter: new PrismaPg({ connectionString: databaseUrl }),
+  });
+}
+
+export function getPrismaClient(): PrismaClient {
+  prismaClient ??= createPrismaClient();
+  return prismaClient;
+}
+
+const prisma = new Proxy({} as PrismaClient, {
+  get(_target, property) {
+    const client = getPrismaClient();
+    const value = Reflect.get(client, property);
+    return typeof value === 'function' ? value.bind(client) : value;
+  },
+});
+
+export default prisma;
+
+export type PrismaTransaction = Prisma.TransactionClient;
+
+export type PrismaDb = PrismaClient | PrismaTransaction;
+
+class ResultRollbackError<TError> extends Error {
+  constructor(readonly result: Result<never, TError>) {
+    super('Transaction rolled back because callback returned Result.err');
+  }
+}
+
+export class UnitOfWork {
+  constructor(private readonly prisma: PrismaClient) {}
+
+  async execute<T>(callback: (tx: PrismaTransaction) => Promise<T>): Promise<T> {
+    return this.prisma.$transaction(callback);
+  }
+
+  async executeResult<TValue, TError>(
+    callback: (tx: PrismaTransaction) => Promise<Result<TValue, TError>>,
+    options?: { isolationLevel?: Prisma.TransactionIsolationLevel },
+  ): Promise<Result<TValue, TError>> {
+    try {
+      return await this.prisma.$transaction(async (tx) => {
+        const result = await callback(tx);
+        if (!result.ok) {
+          throw new ResultRollbackError(result);
+        }
+
+        return result;
+      }, options);
+    } catch (error) {
+      if (error instanceof ResultRollbackError) {
+        return error.result;
+      }
+
+      throw error;
+    }
+  }
+}