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/story-panel.tsx

@@ -7,6 +7,7 @@ import {
   DragEndEvent,
   DragOverlay,
   DragStartEvent,
+  KeyboardSensor,
   PointerSensor,
   useSensor,
   useSensors,
@@ -17,6 +18,7 @@ import {
   useSortable,
   horizontalListSortingStrategy,
   arrayMove,
+  sortableKeyboardCoordinates,
 } from '@dnd-kit/sortable'
 import { CSS } from '@dnd-kit/utilities'
 import { toast } from 'sonner'
@@ -135,7 +137,7 @@ function StoryDetailSheet({
   const [state, formAction] = useActionState(
     async (_prev: unknown, fd: FormData) => {
       const result = await updateStoryAction(_prev, fd)
-      if (result?.success) onClose()
+      if (result?.success) { toast.success('Story opgeslagen'); onClose() }
       return result
     },
     undefined
@@ -143,7 +145,9 @@ function StoryDetailSheet({
 
   function handleDelete() {
     startDeleteTransition(async () => {
-      await deleteStoryAction(story.id)
+      const result = await deleteStoryAction(story.id)
+      if (result && 'error' in result) toast.error(result.error ?? 'Verwijderen mislukt')
+      else toast.success('Story verwijderd')
       onClose()
     })
   }
@@ -279,7 +283,7 @@ function CreateStoryForm({
   const [state, formAction] = useActionState(
     async (_prev: unknown, fd: FormData) => {
       const result = await createStoryAction(_prev, fd)
-      if (result?.success) onDone()
+      if (result?.success) { toast.success('Story aangemaakt'); onDone() }
       return result
     },
     undefined
@@ -346,7 +350,10 @@ export function StoryPanel({ productId, storiesByPbi, isDemo }: StoryPanelProps)
     p => grouped[p].length > 0 || creatingPriority === 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)