feat(auth): add user referral system with invite codes

Generate unique referral codes for users
Allow new users to register with a referral code
Display referral stats and invite link in user profile

backend/src/server.ts

@@ -5,6 +5,7 @@ import Fastify from 'fastify';
 import type { FastifyReply, FastifyRequest } from 'fastify';
 import { mkdir } from 'node:fs/promises';
 import {
+  getReferralSummary,
   getUserBySessionToken,
   loginUser,
   logoutSession,
@@ -239,6 +240,17 @@ app.patch('/api/auth/me', async (request, reply) => {
   return { user: await updateCurrentUser(user.id, payload, requestLocale(request)) };
 });
 
+app.get('/api/auth/referral', async (request, reply) => {
+  const token = getBearerToken(request.headers.authorization);
+  const user = token ? await getUserBySessionToken(token) : null;
+
+  if (!user) {
+    return reply.code(401).send({ message: await serverMessage(requestLocale(request), 'loginRequired') });
+  }
+
+  return { referral: await getReferralSummary(user.id) };
+});
+
 app.post('/api/auth/logout', async (request, reply) => {
   const token = getBearerToken(request.headers.authorization);
   if (token) {