feat(11-03): cpvDivisions column — normalizer + backfill migration

Adds Tender.cpvDivisions String[] (@@index Gin) derived at ingestion time
via cpv-catalog.ts's divisionOf() — replaces exact-match cpvCodes
comparison with a typesafe, GIN-indexable hasSome target (FILTER-03,
Pitfall 2). Backfill migration 20260721150000_tender_cpv_divisions_backfill
applied locally: 1612/1671 rows populated across all observed divisions
(741 rows carry division '45' — Bauarbeiten); idempotent (second run:
UPDATE 0, ADD COLUMN IF NOT EXISTS / CREATE INDEX IF NOT EXISTS both skip
cleanly). Applied via docker exec psql + `prisma migrate resolve
--applied` + `prisma generate` against the local dev DB only — no
Docker deploy on the test server.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/api/prisma/schema.prisma

@@ -269,6 +269,7 @@ model Tender {
   title          String
   buyerName      String?
   cpvCodes       String[]  @default([])
+  cpvDivisions   String[]  @default([]) // FILTER-03: normalized 2-digit CPV divisions (hasSome-filterable, Pitfall 2)
   region         String?
   plz            String?
   bundesland     String?
@@ -287,6 +288,7 @@ model Tender {
   @@index([deadlineAt])
   @@index([publishedAt])
   @@index([bundesland]) // FILTER-02: post-backfill Bundesland-Filter-Performance
+  @@index([cpvDivisions], type: Gin) // FILTER-03: post-backfill CPV-Divisions-Filter-Performance (hasSome)
   // Deliberately NO tenant column and NO tenant index — this is global data (D-03)
 }