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>

prisma/seed-data/parse-backlog.ts

@@ -21,7 +21,7 @@ export type ParsedMilestone = {
   title: string
   goal: string
   priority: 1 | 2 | 3 | 4
-  sprint_status: 'ACTIVE' | 'COMPLETED'
+  sprint_status: 'OPEN' | 'CLOSED'
   sort_order: number
   stories: ParsedStory[]
 }
@@ -66,19 +66,19 @@ const MILESTONE_GOAL: Record<string, string> = {
 }
 
 const MILESTONE_SPRINT_STATUS: Record<string, ParsedMilestone['sprint_status']> = {
-  M0: 'COMPLETED',
-  M1: 'COMPLETED',
-  M2: 'COMPLETED',
-  M3: 'COMPLETED',
-  'M3.5': 'COMPLETED',
-  M4: 'COMPLETED',
-  M5: 'COMPLETED',
-  M6: 'COMPLETED',
-  M7: 'COMPLETED',
-  M8: 'COMPLETED',
-  M9: 'COMPLETED',
-  M10: 'COMPLETED',
-  M11: 'COMPLETED',
+  M0: 'CLOSED',
+  M1: 'CLOSED',
+  M2: 'CLOSED',
+  M3: 'CLOSED',
+  'M3.5': 'CLOSED',
+  M4: 'CLOSED',
+  M5: 'CLOSED',
+  M6: 'CLOSED',
+  M7: 'CLOSED',
+  M8: 'CLOSED',
+  M9: 'CLOSED',
+  M10: 'CLOSED',
+  M11: 'CLOSED',
 }
 
 const MILESTONE_KEY = /^(?:M[\d.]+|PBI-\d+)$/
@@ -154,7 +154,7 @@ export async function loadBacklog(
         title,
         goal: MILESTONE_GOAL[key] ?? title,
         priority: MILESTONE_PRIORITY[key] ?? 4,
-        sprint_status: MILESTONE_SPRINT_STATUS[key] ?? 'COMPLETED',
+        sprint_status: MILESTONE_SPRINT_STATUS[key] ?? 'CLOSED',
         sort_order: milestones.length + 1,
         stories: [],
       }