feat: ST-101-ST-110 M1 producten, PBI backlog, iconen en PWA manifest

- Product aanmaken/bewerken/archiveren/herstellen (ST-101, ST-103)
- SplitPane component met versleepbare splitter en localStorage (ST-104)
- PanelNavBar herbruikbaar paneelheader component (ST-105)
- PbiList met prioriteitsgroepen, inline aanmaken, filter en verwijderen (ST-106-ST-110)
- StoryPanel placeholder rechter paneel met selectie via Zustand (ST-109)
- App iconen geinstalleerd: favicon, apple-icon, PWA manifest (192/512px)
- AppIcon SVG component in navigatiebar
- Root layout metadata bijgewerkt naar Nederlands

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

actions/pbis.ts

@@ -0,0 +1,112 @@
+'use server'
+
+import { revalidatePath } from 'next/cache'
+import { cookies } from 'next/headers'
+import { getIronSession } from 'iron-session'
+import { z } from 'zod'
+import { prisma } from '@/lib/prisma'
+import { SessionData, sessionOptions } from '@/lib/session'
+
+async function getSession() {
+  return getIronSession<SessionData>(await cookies(), sessionOptions)
+}
+
+async function verifyProductOwnership(productId: string, userId: string) {
+  return prisma.product.findFirst({ where: { id: productId, user_id: userId } })
+}
+
+const createPbiSchema = z.object({
+  productId: z.string(),
+  title: z.string().min(1, 'Titel is verplicht').max(200),
+  priority: z.coerce.number().int().min(1).max(4),
+})
+
+const updatePbiSchema = z.object({
+  id: z.string(),
+  title: z.string().min(1, 'Titel is verplicht').max(200),
+  description: z.string().max(2000).optional(),
+  priority: z.coerce.number().int().min(1).max(4),
+})
+
+export async function createPbiAction(_prevState: unknown, formData: FormData) {
+  const session = await getSession()
+  if (!session.userId) return { error: 'Niet ingelogd' }
+  if (session.isDemo) return { error: 'Niet beschikbaar in demo-modus' }
+
+  const parsed = createPbiSchema.safeParse({
+    productId: formData.get('productId'),
+    title: formData.get('title'),
+    priority: formData.get('priority'),
+  })
+  if (!parsed.success) return { error: parsed.error.flatten().fieldErrors }
+
+  const product = await verifyProductOwnership(parsed.data.productId, session.userId)
+  if (!product) return { error: 'Product niet gevonden' }
+
+  const last = await prisma.pbi.findFirst({
+    where: { product_id: parsed.data.productId, priority: parsed.data.priority },
+    orderBy: { sort_order: 'desc' },
+  })
+  const sort_order = (last?.sort_order ?? 0) + 1.0
+
+  const pbi = await prisma.pbi.create({
+    data: {
+      product_id: parsed.data.productId,
+      title: parsed.data.title,
+      priority: parsed.data.priority,
+      sort_order,
+    },
+  })
+
+  revalidatePath(`/products/${parsed.data.productId}`)
+  return { success: true, pbi }
+}
+
+export async function updatePbiAction(_prevState: unknown, formData: FormData) {
+  const session = await getSession()
+  if (!session.userId) return { error: 'Niet ingelogd' }
+  if (session.isDemo) return { error: 'Niet beschikbaar in demo-modus' }
+
+  const parsed = updatePbiSchema.safeParse({
+    id: formData.get('id'),
+    title: formData.get('title'),
+    description: formData.get('description') || undefined,
+    priority: formData.get('priority'),
+  })
+  if (!parsed.success) return { error: parsed.error.flatten().fieldErrors }
+
+  const pbi = await prisma.pbi.findFirst({
+    where: { id: parsed.data.id },
+    include: { product: true },
+  })
+  if (!pbi || pbi.product.user_id !== session.userId) return { error: 'PBI niet gevonden' }
+
+  await prisma.pbi.update({
+    where: { id: parsed.data.id },
+    data: {
+      title: parsed.data.title,
+      description: parsed.data.description ?? null,
+      priority: parsed.data.priority,
+    },
+  })
+
+  revalidatePath(`/products/${pbi.product_id}`)
+  return { success: true }
+}
+
+export async function deletePbiAction(id: string) {
+  const session = await getSession()
+  if (!session.userId) return { error: 'Niet ingelogd' }
+  if (session.isDemo) return { error: 'Niet beschikbaar in demo-modus' }
+
+  const pbi = await prisma.pbi.findFirst({
+    where: { id },
+    include: { product: true },
+  })
+  if (!pbi || pbi.product.user_id !== session.userId) return { error: 'PBI niet gevonden' }
+
+  await prisma.pbi.delete({ where: { id } })
+
+  revalidatePath(`/products/${pbi.product_id}`)
+  return { success: true }
+}