feat: ST-601-ST-612 M6 polish, beveiliging en launch-ready

- ST-601/602: loading skeletons en error boundary
- ST-603: Sonner toasts op alle CRUD-operaties
- ST-604: DemoTooltip op uitgeschakelde knoppen
- ST-605: KeyboardSensor dnd-kit, Escape sluit modals
- ST-606: min-width banner < 1024px
- ST-607: WCAG AA aria-labels en skip link
- ST-608: rate limiting login (10/min) en registratie (5/uur)
- ST-609: security integratietests cross-user toegang (7 tests)
- ST-610: GitHub Actions CI/CD workflow
- ST-611: README met quickstart, deployment en API-docs
- ST-612: Lars-flow acceptatiechecklist
- fix: settings toont gebruikersnaam i.p.v. interne id
- fix: seed idempotent, testdata altijd gekoppeld aan demo-gebruiker

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

prisma/seed.ts

@@ -62,11 +62,21 @@ async function main() {
 
   console.log(`Main user: ${user.username} (id: ${user.id})`)
 
-  // Create the Scrum4Me product (using the product backlog doc data)
-  const product = await prisma.product.upsert({
-    where: { user_id_name: { user_id: demo.id, name: 'DevPlanner' } },
-    update: {},
-    create: {
+  // Reset demo product data — delete in dependency order to avoid FK violations
+  const existingProducts = await prisma.product.findMany({ where: { user_id: demo.id }, select: { id: true } })
+  for (const p of existingProducts) {
+    // Stories reference product_id directly (no cascade), so delete PBIs first (cascades to stories via pbi_id)
+    const existingPbis = await prisma.pbi.findMany({ where: { product_id: p.id }, select: { id: true } })
+    for (const pbi of existingPbis) {
+      await prisma.story.deleteMany({ where: { pbi_id: pbi.id } })
+    }
+    await prisma.pbi.deleteMany({ where: { product_id: p.id } })
+    await prisma.sprint.deleteMany({ where: { product_id: p.id } })
+  }
+  await prisma.product.deleteMany({ where: { user_id: demo.id } })
+
+  const product = await prisma.product.create({
+    data: {
       user_id: demo.id,
       name: 'DevPlanner',
       description: 'Een lichtgewicht Scrum-gebaseerde projectplanner voor solo developers en kleine Scrum Teams.',
@@ -76,7 +86,7 @@ async function main() {
     },
   })
 
-  console.log(`Product created: ${product.name} (id: ${product.id})`)
+  console.log(`Product created: ${product.name} (id: ${product.id}, owner: demo)`)
 
   // PBI data from the product backlog document
   const pbis = [