feat(PBI-63): meerdere sprints per product + EXCLUDED + sprint-switcher (#161)

- Sprint lifecycle: ACTIVE→OPEN, COMPLETED→CLOSED, +ARCHIVED (FAILED behouden)
- TaskStatus: +EXCLUDED (overgeslagen door agent-loop via bestaande TO_DO filter)
- Cookie-gebaseerde actieve sprint per product (lib/active-sprint.ts)
- Route splitsen: /products/[id]/sprint/[sprintId] + /sprint redirect-page
- NavBar: gestapelde product/sprint dropdowns + BUILDING-badge derivatie
- Backlog selectie-modus + nieuwe-sprint-dialog (createSprintWithPbisAction)
- Migratie 20260507210000_sprint_lifecycle: ALTER TYPE RENAME (geen data-rewrite)
- Version bump 1.0.0 → 1.2.0

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

app/api/realtime/solo/route.ts

@@ -261,7 +261,7 @@ export async function GET(request: NextRequest) {
 async function prisma_sprint_findActive(productId: string): Promise<{ id: string } | null> {
   const { prisma } = await import('@/lib/prisma')
   return prisma.sprint.findFirst({
-    where: { product_id: productId, status: 'ACTIVE' },
+    where: { product_id: productId, status: 'OPEN' },
     select: { id: true },
     orderBy: { created_at: 'desc' },
   })