feat(PBI-79/ST-1334): user-settings pendingSprintDraft-slot

- lib/user-settings.ts: nieuw workflow.pendingSprintDraft veld met
  compacte intent-shape (pbiIntent + per-PBI storyOverrides).
- actions/sprint-draft.ts: setPendingSprintDraftAction +
  clearPendingSprintDraftAction met product-membership-check + Zod-validatie.
- stores/user-settings/store.ts: setPendingSprintDraft / clearPendingSprintDraft
  optimistic acties + fine-grained mutators upsertPbiIntent / upsertStoryOverride.
  Sprint-draft actions worden dynamisch geïmporteerd zodat jsdom-tests
  zonder DATABASE_URL niet falen.
- Tests: nieuwe sprint-draft.test.ts (action-laag), uitbreiding
  user-settings store-tests (5 nieuwe cases) en schema-tests (4 cases).

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

lib/user-settings.ts

@@ -48,13 +48,36 @@ const LayoutPrefs = z.object({
   activeSprints: z.record(z.string(), z.string().nullable()).optional(),
 }).strict()
 
+const PbiIntent = z.enum(['all', 'none'])
+
+const StoryOverrides = z.object({
+  add: z.array(z.string()),
+  remove: z.array(z.string()),
+}).strict()
+
+const PendingSprintDraftSchema = z.object({
+  goal: z.string().min(1),
+  startAt: z.string().datetime().optional(),
+  endAt: z.string().datetime().optional(),
+  pbiIntent: z.record(z.string(), PbiIntent).default({}),
+  storyOverrides: z.record(z.string(), StoryOverrides).default({}),
+}).strict()
+
+const WorkflowPrefs = z.object({
+  pendingSprintDraft: z.record(z.string(), PendingSprintDraftSchema).optional(),
+}).strict()
+
 export const UserSettingsSchema = z.object({
   views: ViewsPrefs.optional(),
   devTools: DevToolsPrefs.optional(),
   layout: LayoutPrefs.optional(),
+  workflow: WorkflowPrefs.optional(),
 }).strict()
 
 export type UserSettings = z.infer<typeof UserSettingsSchema>
+export type PendingSprintDraft = z.infer<typeof PendingSprintDraftSchema>
+export type PbiIntent = z.infer<typeof PbiIntent>
+export type StoryOverrides = z.infer<typeof StoryOverrides>
 
 export const DEFAULT_USER_SETTINGS: UserSettings = {}