Automate prisma db push during build for deployment

[rowan-stein]

Problem

After deploying to Vercel, the database tables don't exist because prisma db push was never run against the production database. This causes "Access Denied" on sign-in with error:

The table `public.users` does not exist in the current database.

Fix

Add prisma db push to the build script in package.json so it runs automatically on every Vercel deployment. prisma db push is idempotent — it only applies changes if the schema differs from the database, so it's safe to run on every build.

Change:

"build": "next build"

To:

"build": "prisma db push && next build"

This ensures the database schema is always in sync with the Prisma schema before the app builds.