feat: ProductMember — team management for product backlogs

- Add ProductMember model (many-to-many User ↔ Product)
- Add productAccessFilter helper (owner OR member OR clause)
- Replace all ownership checks across actions and API routes
- Add addProductMemberAction / removeProductMemberAction / leaveProductAction
- Add TeamManager component in product settings (owner adds/removes Developers)
- Add LeaveProductButton in user settings (member leaves a product team)
- Regenerate Prisma Client after schema migration

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

app/(app)/products/[id]/settings/page.tsx

@@ -5,6 +5,7 @@ import { SessionData, sessionOptions } from '@/lib/session'
 import { prisma } from '@/lib/prisma'
 import { ProductForm } from '@/components/products/product-form'
 import { ArchiveProductButton } from '@/components/products/archive-product-button'
+import { TeamManager } from '@/components/products/team-manager'
 import { updateProductAction } from '@/actions/products'
 import Link from 'next/link'
 
@@ -20,9 +21,17 @@ export default async function ProductSettingsPage({ params }: Props) {
 
   const product = await prisma.product.findFirst({
     where: { id, user_id: session.userId },
+    include: {
+      members: {
+        include: { user: { select: { id: true, username: true } } },
+        orderBy: { created_at: 'asc' },
+      },
+    },
   })
   if (!product) notFound()
 
+  const members = product.members.map(m => ({ id: m.user.id, username: m.user.username }))
+
   return (
     <div className="p-6 max-w-2xl mx-auto w-full">
       <div className="flex items-center gap-3 mb-6">
@@ -45,7 +54,17 @@ export default async function ProductSettingsPage({ params }: Props) {
         }}
       />
 
-      <div className="mt-10 pt-6 border-t border-border">
+      <div className="mt-8 pt-6 border-t border-border space-y-3">
+        <div>
+          <h2 className="text-sm font-medium text-foreground">Team</h2>
+          <p className="text-xs text-muted-foreground mt-0.5">
+            Voeg Developers toe die aan dit product mogen werken. Alleen gebruikers met de rol Developer kunnen worden toegevoegd.
+          </p>
+        </div>
+        <TeamManager productId={id} members={members} />
+      </div>
+
+      <div className="mt-8 pt-6 border-t border-border">
         <h2 className="text-sm font-medium text-foreground mb-3">Gevaarlijke zone</h2>
         <div className="bg-error-container/30 border border-error/20 rounded-xl p-4 flex items-center justify-between gap-4">
           <div>