Fix Vercel deployment configuration conflict

[robdimarco-atxp]

Summary

Fixes Vercel deployment error: "The functions property cannot be used in conjunction with the builds property"

Problem

Vercel deployment was failing because our vercel.json configuration was using both:

• Legacy builds property (Vercel v1/v2 style)
• Modern functions property (current Vercel standard)

These two configuration approaches are incompatible in modern Vercel deployments.

Solution

• Removed legacy builds array - No longer needed as Vercel auto-detects TypeScript/Node.js files
• Kept modern functions property - Essential for setting maxDuration: 30 on serverless function
• Preserved routes and installCommand - Required for single-service architecture

Configuration Changes

Before:

{
  "builds": [{"src": "backend/server.ts", "use": "@vercel/node", ...}],
  "functions": {"backend/server.ts": {"maxDuration": 30}}
}

After:

{
  "routes": [{"src": "/(.*)", "dest": "/backend/server.ts"}],
  "functions": {"backend/server.ts": {"maxDuration": 30}}
}

How it Works Now

1. Auto-detection: Vercel automatically detects backend/server.ts as Node.js serverless function
2. Single route: All requests route to Express server (both API and static frontend)
3. Build process: npm run setup handles dependency installation and building
4. Function timeout: 30-second limit configured for serverless function

Test Plan

• Vercel configuration validated (no syntax conflicts)
• Single-service architecture preserved (Express serves both API and React frontend)
• Build process remains unchanged (npm run setup)

This should resolve the Vercel deployment error and allow successful deployment of the single-service ATXP Express application.

Linear Issue: https://linear.app/novellum/issue/ATXP-258/add-one-click-deploy-for-atxp-expresso-example

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