feat: implement complex user invitation handler with tests and configuration

apps/backend/test/support/prisma.mock.ts

@@ -0,0 +1,33 @@
+import { mock } from 'bun:test';
+import { createPrismaMock } from 'bun-mock-prisma';
+
+import type { PrismaClient } from '@/generated/prisma/client';
+import type { PrismaClientMock } from 'bun-mock-prisma';
+
+export const prismaMock = createPrismaMock<PrismaClient>() as PrismaClientMock<PrismaClient>;
+export const sendMailMock = mock(async (_input: {
+  to: string;
+  subject: string;
+  html: string;
+  text: string;
+}) => undefined);
+export const transactionMock = mock(async <T>(fn: (tx: PrismaClientMock<PrismaClient>) => Promise<T>) =>
+  fn(prismaMock)
+);
+export const dbMock = {
+  complexUser: prismaMock.complexUser,
+  complex: prismaMock.complex,
+  user: prismaMock.user,
+  complexInvitation: prismaMock.complexInvitation,
+  $transaction: transactionMock,
+};
+
+mock.module('@/lib/prisma', () => ({
+  __esModule: true,
+  db: dbMock,
+}));
+
+mock.module('@/lib/mailer', () => ({
+  __esModule: true,
+  sendMail: sendMailMock,
+}));