feat: Vercel deploy config — auto schema push on build - #12

Adds a vercel-build script to apps/portal/package.json:

"vercel-build": "prisma generate && prisma db push && next build"

Why: Vercel auto-detects and runs the vercel-build script instead of build. This ensures:

• Prisma client is generated fresh each deploy
• Database schema is auto-synced (no manual prisma db push needed)
• Standard recommended pattern for Vercel + Prisma + Neon

No impact on local development — npm run build still just runs next build.