docs+tests(sort-order): update for code-binding order on stories/tasks

- Rewrite docs/patterns/sort-order.md: float-insertion PBI only; story/task
  sort_order = parseCodeNumber(code), never drag/membership mutated
- Update plan-to-pbi-flow.md: sort_order auto, sprint_id param, priority=label
- Update make-plan.md: priority=label, array order = execution order
- Update rest-contract.md: fix sprint-tasks ordering, remove reorder endpoint
- Add ADR-0011: code is bindende volgordesleutel voor stories/taken
- Regenerate docs/INDEX.md via npm run docs
- Remove reorderStoriesAction/reorderTasksAction mocks from backlog tests
- Remove dnd-kit mocks from task-panel test (panel no longer uses dnd)
- Extend materializeIdeaPlanAction test: assert sort_order=parseCodeNumber(code)

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

__tests__/components/backlog/integration.test.tsx

@@ -25,18 +25,16 @@ Object.defineProperty(globalThis, 'localStorage', { value: localStorageMock, wri
 
 // Mock server actions
 vi.mock('@/actions/stories', () => ({
-  reorderStoriesAction: vi.fn().mockResolvedValue({ success: true }),
   reorderPbisAction: vi.fn().mockResolvedValue({ success: true }),
   updatePbiPriorityAction: vi.fn().mockResolvedValue({ success: true }),
 }))
 vi.mock('@/actions/pbis', () => ({ deletePbiAction: vi.fn().mockResolvedValue({ success: true }) }))
-vi.mock('@/actions/tasks', () => ({ reorderTasksAction: vi.fn().mockResolvedValue({ success: true }) }))
 vi.mock('@/actions/user-settings', () => ({
   updateUserSettingsAction: vi.fn().mockResolvedValue({ success: true, settings: {} }),
 }))
 vi.mock('sonner', () => ({ toast: { error: vi.fn(), success: vi.fn() } }))
 
-// Mock dnd-kit
+// Mock dnd-kit (still needed for PBI panel which supports drag-and-drop)
 vi.mock('@dnd-kit/core', () => ({
   DndContext: ({ children }: { children: React.ReactNode }) => <>{children}</>,
   PointerSensor: class {},

__tests__/components/backlog/task-panel.test.tsx

@@ -33,37 +33,8 @@ function setActiveStoryAndTasks(storyId: string | null, tasks: BacklogTask[] = [
 const mockPush = vi.fn()
 vi.mock('next/navigation', () => ({ useRouter: () => ({ push: mockPush }) }))
 
-// Mock reorderTasksAction
-vi.mock('@/actions/tasks', () => ({ reorderTasksAction: vi.fn().mockResolvedValue({ success: true }) }))
 vi.mock('sonner', () => ({ toast: { error: vi.fn(), success: vi.fn() } }))
 
-// Mock dnd-kit to avoid jsdom drag complexity
-vi.mock('@dnd-kit/core', () => ({
-  DndContext: ({ children }: { children: React.ReactNode }) => <>{children}</>,
-  PointerSensor: class {},
-  KeyboardSensor: class {},
-  useSensor: vi.fn(),
-  useSensors: vi.fn(() => []),
-  closestCenter: vi.fn(),
-  DragOverlay: () => null,
-}))
-vi.mock('@dnd-kit/sortable', () => ({
-  SortableContext: ({ children }: { children: React.ReactNode }) => <>{children}</>,
-  useSortable: () => ({
-    attributes: {}, listeners: {}, setNodeRef: vi.fn(),
-    transform: null, transition: undefined, isDragging: false,
-  }),
-  rectSortingStrategy: {},
-  sortableKeyboardCoordinates: {},
-  arrayMove: (arr: unknown[], from: number, to: number) => {
-    const next = [...arr]
-    next.splice(from, 1)
-    next.splice(to, 0, arr[from])
-    return next
-  },
-}))
-vi.mock('@dnd-kit/utilities', () => ({ CSS: { Transform: { toString: () => '' } } }))
-
 import { TaskPanel } from '@/components/backlog/task-panel'
 
 const PRODUCT_ID = 'prod-1'
@@ -141,12 +112,4 @@ describe('TaskPanel', () => {
     expect((btn as HTMLButtonElement).disabled).toBe(true)
   })
 
-  it('cards have no drag listeners in demo mode (whole-card drag disabled)', () => {
-    setActiveStoryAndTasks(STORY_ID, TASKS)
-    // In demo mode, listeners ({} from useSortable mock) are not spread onto the card.
-    // The mock always returns empty listeners, so we just verify the cards render without error.
-    renderPanel(true)
-    expect(screen.getByText('Eerste taak')).toBeTruthy()
-    expect(screen.getByText('Tweede taak')).toBeTruthy()
-  })
 })