feat(ST-1109.5): auto-mark PBI as DONE when all its stories are DONE on sprint close

Extends completeSprintAction's $transaction with PBI status cascade:
- Pre-transaction: identify PBIs touched by this close (via stories.pbi_id),
  fetch each with all its stories
- Skip PBIs already DONE; skip PBIs with 0 stories
- Mark PBI DONE only when every story (post-decision) is DONE — stories
  outside the sprint are evaluated against their current DB status
- Promote-only: never demotes a PBI that becomes "incomplete" again

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

actions/sprints.ts

@@ -171,10 +171,28 @@ export async function completeSprintAction(
 
   const stories = await prisma.story.findMany({
     where: { id: { in: storyIds }, sprint_id: sprintId, product_id: sprint.product_id },
-    select: { id: true },
+    select: { id: true, pbi_id: true },
   })
   if (stories.length !== storyIds.length) return { error: 'Ongeldige Sprint-afronding' }
 
+  const affectedPbiIds = [...new Set(stories.map((s) => s.pbi_id))]
+  const candidatePbis = await prisma.pbi.findMany({
+    where: { id: { in: affectedPbiIds }, status: { not: 'DONE' } },
+    select: { id: true, stories: { select: { id: true, status: true } } },
+  })
+
+  const decisionByStoryId = new Map(entries)
+  const pbiIdsToMarkDone = candidatePbis
+    .filter(
+      (pbi) =>
+        pbi.stories.length > 0 &&
+        pbi.stories.every((s) => {
+          const next = decisionByStoryId.get(s.id) ?? s.status
+          return next === 'DONE'
+        })
+    )
+    .map((p) => p.id)
+
   await prisma.$transaction([
     ...entries.map(([storyId, status]) =>
       prisma.story.update({
@@ -185,6 +203,9 @@ export async function completeSprintAction(
         },
       })
     ),
+    ...pbiIdsToMarkDone.map((id) =>
+      prisma.pbi.update({ where: { id }, data: { status: 'DONE' } })
+    ),
     prisma.sprint.update({
       where: { id: sprintId },
       data: { status: 'COMPLETED', completed_at: new Date() },