feat(PBI-71): UX-fix 'lege sprint' + sprint-switch data-refresh (#175)

- StartSprintButton dialog toont 3-state banner: info met accurate vrije-
  stories count + PBI-context, of waarschuwing als geen PBI geselecteerd
  is, of waarschuwing als de geselecteerde PBI 0 vrije stories heeft
- Voeg sprint_id toe aan BacklogStory/Story/SprintStory + select in PB-
  pagina's en sprint-board mappings, zodat de banner accuraat kan tellen
- createSprintAction: revalidatePath met 'layout' flag voor consistency
  met createSprintWithPbisAction (top-nav 'Sprint' link ververst direct)

Sprint-switch data-refresh op alle relevante pagina's:

- BacklogHydrationWrapper: fingerprint-based re-hydratie zodat PB-data
  na router.refresh opnieuw uit nieuwe initialData komt (was: useEffect
  met lege deps draaide alleen 1x)
- SprintBoardClient: key={sprint.id} forceert remount bij sprint-switch
  zodat lokale sprintStories/sprintStoryIds-state vers ge-init wordt
- Solo (desktop + mobile): gebruik resolveActiveSprint(id) ipv eerste
  OPEN-sprint, plus key={sprint.id} op SoloBoard voor remount

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

app/(app)/products/[id]/page.tsx

@@ -61,6 +61,7 @@ export default async function ProductBacklogPage({ params, searchParams }: Props
         priority: true,
         status: true,
         pbi_id: true,
+        sprint_id: true,
         created_at: true,
       },
     }),

app/(app)/products/[id]/solo/page.tsx

@@ -2,6 +2,7 @@ import { notFound, redirect } from 'next/navigation'
 import { getSession } from '@/lib/auth'
 import { getAccessibleProduct } from '@/lib/product-access'
 import { prisma } from '@/lib/prisma'
+import { resolveActiveSprint } from '@/lib/active-sprint'
 import { getSprintSwitcherData } from '@/lib/sprint-switcher-data'
 import { SoloBoard } from '@/components/solo/solo-board'
 import { NoActiveSprint } from '@/components/solo/no-active-sprint'
@@ -21,9 +22,10 @@ export default async function SoloProductPage({ params }: Props) {
   const product = await getAccessibleProduct(id, session.userId)
   if (!product) notFound()
 
-  const sprint = await prisma.sprint.findFirst({
-    where: { product_id: id, status: 'OPEN' },
-  })
+  const active = await resolveActiveSprint(id)
+  const sprint = active
+    ? await prisma.sprint.findFirst({ where: { id: active.id, product_id: id } })
+    : null
 
   const switcherData = await getSprintSwitcherData(id, { activeSprintId: sprint?.id ?? null })
 
@@ -126,6 +128,7 @@ export default async function SoloProductPage({ params }: Props) {
       {switcherBar}
       <div className="flex-1 min-h-0">
         <SoloBoard
+          key={sprint.id}
           productId={id}
           sprintGoal={sprint.sprint_goal}
           tasks={tasks}

app/(app)/products/[id]/sprint/[sprintId]/page.tsx

@@ -94,6 +94,7 @@ export default async function SprintBoardPage({ params, searchParams }: Props) {
     description: s.description,
     acceptance_criteria: s.acceptance_criteria,
     pbi_id: s.pbi_id,
+    sprint_id: s.sprint_id,
     created_at: s.created_at,
     priority: s.priority,
     status: s.status,
@@ -144,6 +145,7 @@ export default async function SprintBoardPage({ params, searchParams }: Props) {
         description: s.description,
         acceptance_criteria: s.acceptance_criteria,
         pbi_id: s.pbi_id,
+        sprint_id: s.sprint_id,
         created_at: s.created_at,
         priority: s.priority,
         status: s.status,
@@ -191,6 +193,7 @@ export default async function SprintBoardPage({ params, searchParams }: Props) {
 
       <div className="flex-1 overflow-hidden">
         <SprintBoardClient
+          key={sprint.id}
           productId={id}
           sprintId={sprint.id}
           stories={sprintStoryItems}

app/(mobile)/m/products/[id]/page.tsx

@@ -51,6 +51,7 @@ export default async function MobileProductBacklogPage({ params, searchParams }:
         priority: true,
         status: true,
         pbi_id: true,
+        sprint_id: true,
         created_at: true,
       },
     }),

app/(mobile)/m/products/[id]/solo/page.tsx

@@ -8,6 +8,7 @@ import { notFound } from 'next/navigation'
 import { getAccessibleProduct } from '@/lib/product-access'
 import { prisma } from '@/lib/prisma'
 import { requireSession } from '@/lib/auth-guard'
+import { resolveActiveSprint } from '@/lib/active-sprint'
 import { SoloBoard } from '@/components/solo/solo-board'
 import { NoActiveSprint } from '@/components/solo/no-active-sprint'
 import type { SoloTask } from '@/components/solo/solo-board'
@@ -24,9 +25,10 @@ export default async function MobileSoloProductPage({ params }: Props) {
   const product = await getAccessibleProduct(id, session.userId)
   if (!product) notFound()
 
-  const sprint = await prisma.sprint.findFirst({
-    where: { product_id: id, status: 'OPEN' },
-  })
+  const active = await resolveActiveSprint(id)
+  const sprint = active
+    ? await prisma.sprint.findFirst({ where: { id: active.id, product_id: id } })
+    : null
 
   if (!sprint) {
     return (
@@ -112,6 +114,7 @@ export default async function MobileSoloProductPage({ params }: Props) {
 
   return (
     <SoloBoard
+      key={sprint.id}
       productId={id}
       sprintGoal={sprint.sprint_goal}
       tasks={tasks}