fix: auto-detect baseURL for Better Auth in production

apps/web/src/lib/auth.ts

@@ -3,9 +3,16 @@ import { betterAuth } from 'better-auth';
 import { prismaAdapter } from 'better-auth/adapters/prisma';
 import { sendVerificationEmail } from './email';
 
+// Determine base URL: use env var, or Vercel URL, or default to production
+const getBaseURL = () => {
+  if (process.env.BETTER_AUTH_URL) return process.env.BETTER_AUTH_URL;
+  if (process.env.VERCEL_URL) return `https://${process.env.VERCEL_URL}`;
+  return 'https://tpmjs.com';
+};
+
 export const auth = betterAuth({
   secret: process.env.BETTER_AUTH_SECRET,
-  baseURL: process.env.BETTER_AUTH_URL,
+  baseURL: getBaseURL(),
   database: prismaAdapter(prisma, {
     provider: 'postgresql',
   }),