feat(PBI-75): sprint task-edit client-side via workspace-store (#183)

Klik op een taak in het sprint-scherm opent de edit-dialog nu
client-side via setActiveTask op de sprint-workspace-store.
Geen URL-navigatie, geen volledige server re-render — alleen
GET /api/tasks/{id} voor het detail. SSE propageert server-saves
automatisch terug.

- TaskDialog: optionele onClose/onSaved callbacks (closePath
  optional gemaakt — backwards compatible)
- SprintTaskDialogMount: nieuwe client-component die
  selectActiveTask consumeert en TaskDialog rendert
- SprintUrlTaskSync: deeplink (?editTask=<id>) → store
- Sprint page: mounts toegevoegd, editTask searchParam +
  EditTaskLoader-Suspense verwijderd
- TaskList.openEditDialog roept setActiveTask aan ipv router.push
- Vitest integratie-test voor SprintTaskDialogMount

Out-of-scope (follow-up PBIs): newTask-flow, mobile, product-backlog.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/_components/tasks/task-dialog.tsx

@@ -60,7 +60,9 @@ interface TaskDialogProps {
   task?: TaskDialogTask
   storyId?: string
   productId: string
-  closePath: string
+  closePath?: string
+  onClose?: () => void
+  onSaved?: (taskId: string) => void
   isDemo?: boolean
 }
 
@@ -81,7 +83,7 @@ const textareaClass = cn(
   'overflow-y-auto',
 )
 
-export function TaskDialog({ task, storyId, productId, closePath, isDemo = false }: TaskDialogProps) {
+export function TaskDialog({ task, storyId, productId, closePath, onClose, onSaved, isDemo = false }: TaskDialogProps) {
   const router = useRouter()
   const [isPending, startTransition] = useTransition()
   const [confirmDelete, setConfirmDelete] = useState(false)
@@ -100,11 +102,12 @@ export function TaskDialog({ task, storyId, productId, closePath, isDemo = false
     },
   })
 
-  function handleClose() {
-    router.push(closePath)
+  function close() {
+    if (onClose) { onClose(); return }
+    if (closePath) router.push(closePath)
   }
 
-  const closeGuard = useDirtyCloseGuard(form.formState.isDirty, handleClose)
+  const closeGuard = useDirtyCloseGuard(form.formState.isDirty, close)
   const handleKeyDown = useDialogSubmitShortcut(() => form.handleSubmit(onSubmit)())
 
   function onSubmit(data: TaskInput) {
@@ -117,7 +120,8 @@ export function TaskDialog({ task, storyId, productId, closePath, isDemo = false
 
       if (result.ok) {
         toast.success(isEdit ? 'Taak opgeslagen' : 'Taak aangemaakt')
-        router.push(closePath)
+        onSaved?.(result.task.id)
+        close()
         return
       }
 
@@ -152,7 +156,7 @@ export function TaskDialog({ task, storyId, productId, closePath, isDemo = false
       const result = await deleteTask(task.id, { productId })
       if (result.ok) {
         toast.success('Taak verwijderd')
-        router.push(closePath)
+        close()
         return
       }
       if (result.code === 403) {