feat(PBI-59): Sprint.code (SP-N sequentieel per product) (#153)

Voegt een verplicht code-veld toe aan Sprint, sequentieel per product
(consistent met PBI-N, ST-NNN, T-N).

- **Schema** — `Sprint.code String @db.VarChar(30)` + `@@unique([product_id, code])`
- **Migratie** — voegt kolom toe als nullable, backfillt bestaande sprints
  via `ROW_NUMBER() OVER (PARTITION BY product_id ORDER BY created_at)`
  als `SP-N`, en zet daarna NOT NULL + UNIQUE.
- **Generator** — `generateNextSprintCode(productId)` in lib/code-server.ts
  volgt het patroon van story/pbi/task; createSprintAction gebruikt
  `createWithCodeRetry` voor race-bescherming.
- **Seed** — sprint-counter per product (`SP-1`, `SP-2`, ...).

Zichtbaar in:
- Sprint-header (`Product › Sprint actief · SP-3`)
- JobCard + JobDetailPane voor SPRINT_IMPLEMENTATION jobs
- Insights: VelocityChart x-axis (compacter dan goal-truncated),
  AlignmentTrend tooltip, SprintInfoStrip
- actions/jobs-page.ts: `sprintCode` is weer een echte code i.p.v. null

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

prisma/migrations/20260507195507_add_sprint_code/migration.sql

@@ -0,0 +1,23 @@
+-- PBI-59: Sprint.code (SP-1, SP-2, ...) sequentieel per product
+--
+-- 1. Voeg nullable kolom toe
+-- 2. Backfill bestaande rijen via ROW_NUMBER() per product op created_at
+-- 3. Maak NOT NULL en voeg unieke index toe op (product_id, code)
+
+ALTER TABLE "sprints" ADD COLUMN "code" VARCHAR(30);
+
+WITH numbered AS (
+  SELECT
+    id,
+    product_id,
+    ROW_NUMBER() OVER (PARTITION BY product_id ORDER BY created_at, id) AS n
+  FROM "sprints"
+)
+UPDATE "sprints" s
+SET code = 'SP-' || numbered.n
+FROM numbered
+WHERE s.id = numbered.id;
+
+ALTER TABLE "sprints" ALTER COLUMN "code" SET NOT NULL;
+
+CREATE UNIQUE INDEX "sprints_product_id_code_key" ON "sprints"("product_id", "code");

prisma/schema.prisma

@@ -299,6 +299,7 @@ model Sprint {
   id           String       @id @default(cuid())
   product      Product      @relation(fields: [product_id], references: [id], onDelete: Cascade)
   product_id   String
+  code         String       @db.VarChar(30)
   sprint_goal  String
   status       SprintStatus @default(ACTIVE)
   start_date   DateTime?    @db.Date
@@ -309,6 +310,7 @@ model Sprint {
   tasks        Task[]
   sprint_runs  SprintRun[]
 
+  @@unique([product_id, code])
   @@index([product_id, status])
   @@map("sprints")
 }

prisma/seed.ts

@@ -124,6 +124,7 @@ async function main() {
   console.log(`Loaded backlog: ${milestones.length} milestones, ${milestones.reduce((acc, m) => acc + m.stories.length, 0)} stories`)
 
   let productTaskCounter = 0
+  let sprintCounter = 0
   for (const ms of milestones) {
     const pbi = await prisma.pbi.create({
       data: {
@@ -139,6 +140,7 @@ async function main() {
     const sprint = await prisma.sprint.create({
       data: {
         product_id: product.id,
+        code: `SP-${++sprintCounter}`,
         sprint_goal: `${ms.key} — ${ms.goal}`,
         status: ms.sprint_status,
       },