feat(ST-1109.2): add PbiStatus enum and status field to Pbi model

- New PbiStatus enum (READY/BLOCKED/DONE) for PBI lifecycle tracking
- Pbi.status PbiStatus @default(READY)
- Index on (product_id, status) for filter queries
- Migration: 20260429150643_add_pbi_status
- ERD regenerated via prisma generate

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

prisma/migrations/20260429150643_add_pbi_status/migration.sql

@@ -0,0 +1,8 @@
+-- CreateEnum
+CREATE TYPE "PbiStatus" AS ENUM ('READY', 'BLOCKED', 'DONE');
+
+-- AlterTable
+ALTER TABLE "pbis" ADD COLUMN     "status" "PbiStatus" NOT NULL DEFAULT 'READY';
+
+-- CreateIndex
+CREATE INDEX "pbis_product_id_status_idx" ON "pbis"("product_id", "status");

prisma/schema.prisma

@@ -23,6 +23,12 @@ enum StoryStatus {
   DONE
 }
 
+enum PbiStatus {
+  READY
+  BLOCKED
+  DONE
+}
+
 enum TaskStatus {
   TO_DO
   IN_PROGRESS
@@ -131,12 +137,14 @@ model Pbi {
   description String?
   priority    Int
   sort_order  Float
-  created_at  DateTime @default(now())
-  updated_at  DateTime @updatedAt
+  status      PbiStatus @default(READY)
+  created_at  DateTime  @default(now())
+  updated_at  DateTime  @updatedAt
   stories     Story[]
 
   @@unique([product_id, code])
   @@index([product_id, priority, sort_order])
+  @@index([product_id, status])
   @@map("pbis")
 }