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>

prisma/schema.prisma

@@ -0,0 +1,59 @@
+generator client {
+  provider = "prisma-client-js"
+}
+
+datasource db {
+  provider = "postgresql"
+}
+
+enum FlowStatus {
+  pending
+  running
+  success
+  failed
+  cancelled
+}
+
+model User {
+  id         String    @id @default(cuid())
+  email      String    @unique
+  pwd_hash   String
+  created_at DateTime  @default(now())
+  sessions   Session[]
+  flow_runs  FlowRun[]
+}
+
+model Session {
+  id         String   @id @default(cuid())
+  user_id    String
+  token_hash String   @unique
+  expires_at DateTime
+  user       User     @relation(fields: [user_id], references: [id], onDelete: Cascade)
+}
+
+model FlowRun {
+  id         String     @id @default(cuid())
+  user_id    String
+  flow_key   String
+  status     FlowStatus @default(pending)
+  dry_run    Boolean    @default(false)
+  started_at DateTime   @default(now())
+  ended_at   DateTime?
+  exit_code  Int?
+  user       User       @relation(fields: [user_id], references: [id], onDelete: Cascade)
+  steps      FlowStep[]
+}
+
+model FlowStep {
+  id           String    @id @default(cuid())
+  flow_run_id  String
+  step_index   Int
+  command_key  String
+  args_json    String?
+  stdout       String?
+  stderr       String?
+  exit_code    Int?
+  started_at   DateTime  @default(now())
+  ended_at     DateTime?
+  flow_run     FlowRun   @relation(fields: [flow_run_id], references: [id], onDelete: Cascade)
+}