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>

components/backlog/pbi-list.tsx

@@ -8,6 +8,7 @@ import {
   DragEndEvent,
   DragOverlay,
   DragStartEvent,
+  KeyboardSensor,
   PointerSensor,
   useSensor,
   useSensors,
@@ -18,10 +19,12 @@ import {
   useSortable,
   verticalListSortingStrategy,
   arrayMove,
+  sortableKeyboardCoordinates,
 } from '@dnd-kit/sortable'
 import { CSS } from '@dnd-kit/utilities'
 import { toast } from 'sonner'
 import { Button } from '@/components/ui/button'
+import { DemoTooltip } from '@/components/shared/demo-tooltip'
 import { Input } from '@/components/ui/input'
 import { Badge } from '@/components/ui/badge'
 import { Select, SelectContent, SelectItem, SelectTrigger, SelectValue } from '@/components/ui/select'
@@ -96,6 +99,7 @@ function SortablePbiRow({
         <span
           {...attributes}
           {...listeners}
+          aria-label="Versleep om te sorteren"
           className="mr-2 text-muted-foreground cursor-grab active:cursor-grabbing shrink-0 select-none"
           onClick={(e) => e.stopPropagation()}
         >
@@ -129,7 +133,7 @@ function CreatePbiForm({
   const [state, formAction] = useActionState(
     async (_prev: unknown, fd: FormData) => {
       const result = await createPbiAction(_prev, fd)
-      if (result?.success) onDone()
+      if (result?.success) { toast.success('PBI aangemaakt'); onDone() }
       return result
     },
     undefined
@@ -198,7 +202,10 @@ export function PbiList({ productId, pbis, isDemo }: PbiListProps) {
     p => grouped[p].length > 0 || creatingForPriority === p
   )
 
-  const sensors = useSensors(useSensor(PointerSensor, { activationConstraint: { distance: 5 } }))
+  const sensors = useSensors(
+    useSensor(PointerSensor, { activationConstraint: { distance: 5 } }),
+    useSensor(KeyboardSensor, { coordinateGetter: sortableKeyboardCoordinates })
+  )
 
   function handleDragStart(event: DragStartEvent) {
     setActiveDragId(event.active.id as string)