feat: PostgreSQL support en Vercel CI/CD deployment

- Prisma schema: sqlite → postgresql provider met directUrl
- prisma.config.ts: directUrl toegevoegd
- seed.ts: dynamisch SQLite of PostgreSQL adapter op basis van DATABASE_URL
- ci.yml: preview deploy op PR, productie deploy op push naar main

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

prisma/seed.ts

@@ -1,5 +1,4 @@
 import { PrismaClient } from '@prisma/client'
-import { PrismaBetterSqlite3 } from '@prisma/adapter-better-sqlite3'
 import * as dotenv from 'dotenv'
 import * as path from 'path'
 import * as bcrypt from 'bcryptjs'
@@ -15,9 +14,19 @@ async function main() {
   const url = process.env.DATABASE_URL
   if (!url) throw new Error('DATABASE_URL is not set. Check .env.local')
 
-  // For SQLite: adapter takes a config object with url
-  const adapter = new PrismaBetterSqlite3({ url })
-  prisma = new PrismaClient({ adapter })
+  if (url.startsWith('file:')) {
+    // SQLite (local development)
+    const { PrismaBetterSqlite3 } = await import('@prisma/adapter-better-sqlite3')
+    const adapter = new PrismaBetterSqlite3({ url })
+    prisma = new PrismaClient({ adapter })
+  } else {
+    // PostgreSQL (Neon / production)
+    const { Pool } = await import('pg')
+    const { PrismaPg } = await import('@prisma/adapter-pg')
+    const pool = new Pool({ connectionString: url })
+    const adapter = new PrismaPg(pool)
+    prisma = new PrismaClient({ adapter })
+  }
 
   console.log('Seeding database...')