feat(PBI-74): sprint-workspace-store (Story 9) (#181)

* feat(PBI-74): sprint-workspace-store skelet (Story 9 / T-879)

- stores/sprint-workspace/{types,store,selectors,restore}.ts conform
  product-workspace blueprint
- ContextSlice: activeProduct, activeSprintId, activeStoryId, activeTaskId
- EntitiesSlice: sprintsById, storiesById, tasksById
- RelationsSlice: sprintIdsByProduct, storyIdsBySprint, taskIdsByStory
- LoadingSlice met activeRequestId voor race-safe ensure*Loaded
- SyncSlice: realtimeStatus, lastResyncAt, resyncReason
- Realtime applyRealtimeEvent voor sprint/story/task entities + unknown-event
  fallback, parent-move handling, child-cleanup bij D op sprint/story
- Optimistic mutations: sprint-story-order, sprint-task-order, entity-patch
- LocalStorage hints (storage key sprint-workspace-hints) per product/sprint
- 45 unit-tests groen — verplicht 13 cases uit workspace-store.md §Tests

* feat(PBI-74): sprint hydratie + realtime SSE (Story 9 / T-880)

- app/api/realtime/sprint/route.ts: SSE-stream LISTEN/NOTIFY op
  scrum4me_changes, filter entity ∈ {sprint, story, task} per product_id;
  ready-event, heartbeat 25s, hard-close 240s
- lib/realtime/use-sprint-realtime.ts: client-hook met backoff-reconnect;
  ready-cycle telt; geen close op hidden; setRealtimeStatus
- lib/realtime/use-sprint-workspace-resync.ts: visibility + online triggers
  resyncActiveScopes('visible' | 'reconnect')
- components/sprint/sprint-hydration-wrapper.tsx: hydrateSnapshot via
  useEffect met fingerprint-check; mount realtime + resync
- app/(app)/products/[id]/sprint/[sprintId]/page.tsx: wrap SprintBoardClient
  in SprintHydrationWrapper; bouw SprintWorkspaceTask-shape voor
  tasksByStoryWorkspace en SprintHydrationData voor de wrapper

Schaduw-fase: useSprintStore blijft parallel werken in board components
totdat T-881 die migreert en T-883 de oude store opruimt.

* feat(PBI-74): migreer sprint-board componenten naar workspace-store (Story 9 / T-881)

- TaskList: leest tasks via selectTasksForStory met useShallow; DnD via
  applyOptimisticMutation('sprint-task-order') + settle/rollback
- SprintBacklogLeft: leest stories via selectStoriesForActiveSprint met
  useShallow; props 'stories' verwijderd
- SprintBoardClient: leest sprintStories uit selector i.p.v. lokale state;
  add/remove via direct setState met manuele snapshot-rollback;
  reorder via applyOptimisticMutation('sprint-story-order'); assignee-
  change via store entity-mutation; tasksByStory en sprintStoryIdList
  props weg
- app/(app)/.../sprint/[sprintId]/page.tsx: bouwt SprintHydrationData voor
  wrapper; geeft alleen non-store props door aan SprintBoardClient

useSprintStore wordt nergens meer geïmporteerd — alleen comment-referentie
in SprintHydrationWrapper. Cleanup van het bestand zelf in T-883.

Verify groen (671 tests, typecheck, lint clean).

* feat(PBI-74): read-routes voor sprint-workspace + cache-headers (Story 9 / T-882)

- GET /api/products/[id]/sprints — lijst sprints per product
  (ensureProductSprintsLoaded). force-dynamic, productAccessFilter,
  start_date/end_date naar ISO-date string.
- GET /api/sprints/[id]/workspace — sprint snapshot met sprint-meta,
  stories (incl. taskCount/doneCount/assignee), tasks gegroepeerd per
  story (ensureSprintLoaded). force-dynamic, productAccessFilter via
  product, status-vertaling via taskStatusToApi/storyStatusToApi.

Race-safe loaders (activeRequestId-guard), restore-flow (cascade-restore
via writeProductHint/writeSprintHint/writeStoryHint/writeTaskHint),
resync-laag (useSprintWorkspaceResync visibility + online), unknown-event
filter (isUnknownEntityEvent → resyncActiveScopes('unknown-event')) zijn
allemaal in T-879/T-880 al ingebouwd; T-882 sluit het loop met de
ontbrekende API-endpoints + cache-headers (cache: 'no-store' op fetches,
force-dynamic op routes).

* feat(PBI-74): cleanup oude sprint-store (Story 9 / T-883)

- rm stores/sprint-store.ts — alle componenten lezen nu via
  useSprintWorkspaceStore (T-881 voltooide imports-migratie)
- update SprintHydrationWrapper-comment: schaduw-fase referenties
  verwijderd

Verify: 671 tests groen, typecheck clean, build groen.
Grep useSprintStore = 0.

* docs(PBI-74): update Story 9 status in implementatieplan (T-884)

- Frontmatter: ready-to-execute → in-progress; revision 1 → 2;
  last_updated 2026-05-09 → 2026-05-10
- Stories-tabel: kolom Status toegevoegd (Stories 1-8 DONE via PR #180,
  Story 9 met T-884 op review)
- §Story 9: per-taak status + acceptatie-checklist voor T-884 manuele
  staging-checks
- Aanbeveling-blokje: noteert dat Story 9 vroeger gestart is dan het
  ontwerpdoc adviseerde

components/sprint/sprint-backlog.tsx

@@ -6,6 +6,7 @@ import { useDroppable, useDraggable } from '@dnd-kit/core'
 import { SortableContext, useSortable, verticalListSortingStrategy } from '@dnd-kit/sortable'
 import { CSS } from '@dnd-kit/utilities'
 import { toast } from 'sonner'
+import { useShallow } from 'zustand/react/shallow'
 import { Badge } from '@/components/ui/badge'
 import { Button } from '@/components/ui/button'
 import { Popover, PopoverContent, PopoverTrigger } from '@/components/ui/popover'
@@ -20,7 +21,8 @@ import { DemoTooltip } from '@/components/shared/demo-tooltip'
 import { Tooltip, TooltipContent, TooltipProvider, TooltipTrigger } from '@/components/ui/tooltip'
 import { PRIORITY_BORDER } from '@/components/backlog/backlog-card'
 import { PRIORITY_COLORS } from '@/components/shared/priority-select'
-import { useSprintStore } from '@/stores/sprint-store'
+import { useSprintWorkspaceStore } from '@/stores/sprint-workspace/store'
+import { selectStoriesForActiveSprint } from '@/stores/sprint-workspace/selectors'
 import { claimStoryAction, unclaimStoryAction, reassignStoryAction, claimAllUnassignedInActiveSprintAction } from '@/actions/stories'
 import { PbiDialog, type PbiDialogState } from '@/components/backlog/pbi-dialog'
 import { StoryDialog, type StoryDialogState } from '@/components/backlog/story-dialog'
@@ -236,7 +238,6 @@ function SortableSprintRow({
 
 interface SprintBacklogLeftProps {
   sprintId: string
-  stories: SprintStory[]
   isDemo: boolean
   onRemove: (storyId: string) => void
   onSelect: (storyId: string) => void
@@ -248,19 +249,21 @@ interface SprintBacklogLeftProps {
 }
 
 export function SprintBacklogLeft({
-  sprintId, stories, isDemo, onRemove, onSelect, selectedStoryId,
+  sprintId: _sprintId, isDemo, onRemove, onSelect, selectedStoryId,
   currentUserId, productId, members, onAssigneeChange,
 }: SprintBacklogLeftProps) {
-  const { sprintStoryOrder } = useSprintStore()
+  const orderedStories = useSprintWorkspaceStore(
+    useShallow((s) => selectStoriesForActiveSprint(s) as SprintStory[]),
+  )
   const { setNodeRef, isOver } = useDroppable({ id: 'sprint-zone' })
   const [isPending, startTransition] = useTransition()
   const [storyDialogState, setStoryDialogState] = useState<StoryDialogState | null>(null)
 
-  const unassignedCount = stories.filter(s => s.assignee_id === null).length
+  const unassignedCount = orderedStories.filter(s => (s.assignee_id ?? null) === null).length
   const currentUserUsername = members.find(m => m.userId === currentUserId)?.username ?? null
 
   function handleClaimAll() {
-    const unassigned = stories.filter(s => s.assignee_id === null)
+    const unassigned = orderedStories.filter(s => (s.assignee_id ?? null) === null)
     unassigned.forEach(s => onAssigneeChange(s.id, currentUserId, currentUserUsername))
     startTransition(async () => {
       const result = await claimAllUnassignedInActiveSprintAction(productId)
@@ -273,10 +276,6 @@ export function SprintBacklogLeft({
     })
   }
 
-  const storyMap = Object.fromEntries(stories.map(s => [s.id, s]))
-  const order = sprintStoryOrder[sprintId] ?? stories.map(s => s.id)
-  const orderedStories = order.map(id => storyMap[id]).filter(Boolean)
-
   return (
     <div className="flex flex-col h-full" {...debugProps('sprint-backlog-left', 'SprintBacklogLeft', 'components/sprint/sprint-backlog.tsx')}>
       <PanelNavBar