fix: resolve foreign key constraint by ensuring system user exists in seed script

prisma/seed.ts

@@ -11,6 +11,20 @@ const adapter = new PrismaPg(pool)
 const prisma = new PrismaClient({ adapter })
 
 async function main() {
+  console.log('Ensuring system user exists...')
+  let systemUser = await prisma.user.findUnique({ where: { id: 'system' } })
+  if (!systemUser) {
+    systemUser = await prisma.user.create({
+      data: {
+        id: 'system',
+        username: 'system',
+        email: 'system@localhost',
+        password: 'none',
+        role: 'admin'
+      }
+    })
+  }
+
   console.log('Seeding initial maps from .canvas files...')
   
   const rootDir = resolve(process.cwd())
@@ -59,7 +73,7 @@ async function main() {
           data: {
             id: xflowProject.id,
             name: xflowProject.name,
-            ownerId: xflowProject.ownerId || ownerId,
+            ownerId: ownerId,
             isPublic: true,
             nodes: xflowProject.nodes as any,
             edges: xflowProject.edges as any