feat: Prisma schema, migrations en seed voor auth en audit-log

- Models: User, Session, FlowRun, FlowStep met FlowStatus enum
- prisma.config.ts met DATABASE_URL via @prisma/adapter-pg (Prisma 7 API)
- Initiële migratie applied op ops_dashboard database
- Seed-script voor 1 user via SEED_USER_EMAIL/SEED_USER_PASSWORD env-vars
- lib/prisma.ts als gedeelde singleton client voor Next.js

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

lib/prisma.ts

@@ -0,0 +1,17 @@
+import { PrismaClient } from '@prisma/client'
+import { PrismaPg } from '@prisma/adapter-pg'
+
+function createPrismaClient() {
+  const connectionString = process.env.DATABASE_URL
+  if (!connectionString) {
+    throw new Error('DATABASE_URL environment variable is required')
+  }
+  const adapter = new PrismaPg({ connectionString })
+  return new PrismaClient({ adapter })
+}
+
+const globalForPrisma = globalThis as unknown as { prisma: PrismaClient }
+
+export const prisma = globalForPrisma.prisma ?? createPrismaClient()
+
+if (process.env.NODE_ENV !== 'production') globalForPrisma.prisma = prisma